Move sched_is_before() from sched.c to timer_is_before() in the board
specific timer code. This allows the board code to provide its own
definition.
Also, remove the sched_from_us() and sched_read_time() wrapper
functions and change the callers to directly invoke timer_from_us() /
timer_read_time().
Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
Some architectures are faster passing regular integers than 8bit
integers. Use uint_fast8_t so that the architecture chooses the
appropriate type.
Signed-off-by: Kevin O'Connor <kevin@koconnor.net>