sched/clock: Remove CLOCK_MONOTONIC option from Kconfig

here is the reason:
1.clock_systime_timespec(core function) always exist regardless the setting
2.CLOCK_MONOTONIC is a foundamental clock type required by many places

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>

include/nuttx/clock.h

@@ -182,7 +182,7 @@
 #define TICK2SEC(tick)        (((tick)+(TICK_PER_SEC/2))/TICK_PER_SEC)   /* Rounds */
 
 #if defined(CONFIG_DEBUG_FEATURES) && defined(CONFIG_SYSTEM_TIME64) && \
-    defined(CONFIG_CLOCK_MONOTONIC) && !defined(CONFIG_SCHED_TICKLESS)
+    !defined(CONFIG_SCHED_TICKLESS)
 /* Initial system timer ticks value close to maximum 32-bit value, to test
  * 64-bit system-timer after going over 32-bit value. This is to make errors
  * of casting 64-bit system-timer to 32-bit variables more visible.

include/nuttx/input/touchscreen.h

@@ -204,11 +204,7 @@ static inline uint64_t touch_get_time(void)
 {
   struct timespec ts;
 
-#ifdef CONFIG_CLOCK_MONOTONIC
   clock_gettime(CLOCK_MONOTONIC, &ts);
-#else
-  clock_gettime(CLOCK_REALTIME, &ts);
-#endif
   return 1000000ull * ts.tv_sec + ts.tv_nsec / 1000;
 }
 

include/nuttx/rc/lirc_dev.h

@@ -44,12 +44,7 @@ static inline uint64_t lirc_get_timestamp(void)
 {
   struct timespec ts;
 
-#ifdef CONFIG_CLOCK_MONOTONIC
   clock_gettime(CLOCK_MONOTONIC, &ts);
-#else
-  clock_gettime(CLOCK_REALTIME, &ts);
-#endif
-
   return 1000000000ull * ts.tv_sec + ts.tv_nsec;
 }
 

include/nuttx/sensors/sensor.h

@@ -283,12 +283,7 @@ static inline uint64_t sensor_get_timestamp(void)
 {
   struct timespec ts;
 
-#ifdef CONFIG_CLOCK_MONOTONIC
   clock_gettime(CLOCK_MONOTONIC, &ts);
-#else
-  clock_gettime(CLOCK_REALTIME, &ts);
-#endif
-
   return 1000000ull * ts.tv_sec + ts.tv_nsec / 1000;
 }
 

include/time.h

@@ -71,15 +71,11 @@
  * system time-of-day clock.
  */
 
-#ifdef CONFIG_CLOCK_MONOTONIC
-#  define CLOCK_MONOTONIC  1
-#endif
+#define CLOCK_MONOTONIC    1
 
 /* Monotonic system-wide clock that includes time spent in suspension. */
 
-#ifdef CONFIG_CLOCK_MONOTONIC
-#  define CLOCK_BOOTTIME   2
-#endif
+#define CLOCK_BOOTTIME     2
 
 /* This is a flag that may be passed to the timer_settime() and
  * clock_nanosleep() functions.