sched: Change sched_from_ms() to sched_from_us()

Some code may require micro-second precision so update sched_from_ms()
to use micro-seconds.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/simulator/timer.h

@@ -3,7 +3,7 @@
 
 #include <stdint.h>
 
-uint32_t timer_from_ms(uint32_t ms);
+uint32_t timer_from_us(uint32_t us);
 void timer_periodic(void);
 uint32_t timer_read_time(void);
 uint8_t timer_set_next(uint32_t next);