Replace mktime with timegm in rtc and fs driver

since kernel component should use UTC instead local time

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>
Change-Id: Icf939e1ab0af8e577105f539d2553bc67b3b3d10

sched/clock/clock_initialize.c

@@ -92,7 +92,7 @@ int clock_basetime(FAR struct timespec *tp)
     {
       /* And use the broken-out time to initialize the system time */
 
-      tp->tv_sec  = mktime(&rtctime);
+      tp->tv_sec  = timegm(&rtctime);
       tp->tv_nsec = nsecs;
     }