Patch 6ba1b912 hrtimer: switch
sys_nanosleep to hrtimer breaks dynamic tick. All usleep calls
will fail as the next_timer_interrupt currently does not scan
hrtimer queues. This means the system will be potentially
asleep in the idle mode when the next hrtimer is supposed to
run. Until hrtimer_next_interrupt is implemented, we'll use
the old sys_nanosleep.