Elimate use of the non-standard type systime_t and replace it the equivalent, standard type clock_t

Squashed commit of the following:

    sched:  Rename all use of system_t to clock_t.
    syscall:  Rename all use of system_t to clock_t.
    net:  Rename all use of system_t to clock_t.
    libs:  Rename all use of system_t to clock_t.
    fs:  Rename all use of system_t to clock_t.
    drivers:  Rename all use of system_t to clock_t.
    arch:  Rename all use of system_t to clock_t.
    include:  Remove definition of systime_t; rename all use of system_t to clock_t.

sched/clock/clock.h

@@ -98,10 +98,10 @@ void weak_function clock_timer(void);
 
 int  clock_abstime2ticks(clockid_t clockid,
                          FAR const struct timespec *abstime,
-                         FAR ssystime_t *ticks);
+                         FAR sclock_t *ticks);
 int  clock_time2ticks(FAR const struct timespec *reltime,
-                      FAR ssystime_t *ticks);
-int  clock_ticks2time(ssystime_t ticks, FAR struct timespec *reltime);
+                      FAR sclock_t *ticks);
+int  clock_ticks2time(sclock_t ticks, FAR struct timespec *reltime);
 void clock_timespec_add(FAR const struct timespec *ts1,
                         FAR const struct timespec *ts2,
                         FAR struct timespec *ts3);

sched/clock/clock_abstime2ticks.c

@@ -99,7 +99,7 @@ static long compare_timespec(FAR const struct timespec *a,
  ****************************************************************************/
 
 int clock_abstime2ticks(clockid_t clockid, FAR const struct timespec *abstime,
-                        FAR ssystime_t *ticks)
+                        FAR sclock_t *ticks)
 {
   struct timespec currtime;
   struct timespec reltime;

sched/clock/clock_initialize.c

@@ -188,7 +188,7 @@ static void clock_inittime(void)
     {
       struct timespec ts;
 
-      (void)clock_ticks2time((ssystime_t)g_system_timer, &ts);
+      (void)clock_ticks2time((sclock_t)g_system_timer, &ts);
 
       /* Adjust base time to hide initial timer ticks. */
 

sched/clock/clock_systimer.c

@@ -88,7 +88,7 @@
  *
  ****************************************************************************/
 
-systime_t clock_systimer(void)
+clock_t clock_systimer(void)
 {
 #ifdef CONFIG_SCHED_TICKLESS
 # ifdef CONFIG_SYSTEM_TIME64
@@ -123,14 +123,14 @@ systime_t clock_systimer(void)
   /* Convert to a 64- then a 32-bit value */
 
   tmp = USEC2TICK(1000000 * (uint64_t)ts.tv_sec + (uint64_t)ts.tv_nsec / 1000);
-  return (systime_t)(tmp & TIMER_MASK32);
+  return (clock_t)(tmp & TIMER_MASK32);
 
 # endif /* CONFIG_SYSTEM_TIME64 */
 #else /* CONFIG_SCHED_TICKLESS */
 # ifdef CONFIG_SYSTEM_TIME64
 
-  systime_t sample;
-  systime_t verify;
+  clock_t sample;
+  clock_t verify;
 
   /* 64-bit accesses are not atomic on most architectures.  The following
    * loop samples the 64-bit timer twice and loops in the rare event that

sched/clock/clock_systimespec.c

@@ -173,9 +173,9 @@ int clock_systimespec(FAR struct timespec *ts)
       uint64_t secs;
       uint64_t nsecs;
 #else
-      systime_t msecs;
-      systime_t secs;
-      systime_t nsecs;
+      clock_t msecs;
+      clock_t secs;
+      clock_t nsecs;
 #endif
 
       /* Get the time since power-on in seconds and milliseconds */

sched/clock/clock_ticks2time.c

@@ -63,9 +63,9 @@
  *
  ****************************************************************************/
 
-int clock_ticks2time(ssystime_t ticks, FAR struct timespec *reltime)
+int clock_ticks2time(sclock_t ticks, FAR struct timespec *reltime)
 {
-  ssystime_t remainder;
+  sclock_t remainder;
 
   reltime->tv_sec  = ticks / TICK_PER_SEC;
   remainder        = ticks - TICK_PER_SEC * reltime->tv_sec;

sched/clock/clock_time2ticks.c

@@ -68,7 +68,7 @@
  ****************************************************************************/
 
 int clock_time2ticks(FAR const struct timespec *reltime,
-                     FAR ssystime_t *ticks)
+                     FAR sclock_t *ticks)
 {
 #ifdef CONFIG_HAVE_LONG_LONG
   int64_t relnsec;
@@ -84,7 +84,7 @@ int clock_time2ticks(FAR const struct timespec *reltime,
    * that is greater than or equal to the exact number of tick.
    */
 
-  *ticks = (ssystime_t)((relnsec + NSEC_PER_TICK - 1) / NSEC_PER_TICK);
+  *ticks = (sclock_t)((relnsec + NSEC_PER_TICK - 1) / NSEC_PER_TICK);
   return OK;
 #else
   int32_t relusec;
@@ -111,7 +111,7 @@ int clock_time2ticks(FAR const struct timespec *reltime,
    * that is greater than or equal to the exact number of tick.
    */
 
-  *ticks = (ssystime_t)((relusec + USEC_PER_TICK - 1) / USEC_PER_TICK);
+  *ticks = (sclock_t)((relusec + USEC_PER_TICK - 1) / USEC_PER_TICK);
   return OK;
 #endif
 }