Make sure PWMs are running in sync.

The 3 (red, green, blue) PWMs were sometimes running out of sync,
depending on the notification LED color flow and timing.

Make sure they are running in sync by
- adjusting the PWM atomically (that is, not adjust each one within its
  own worker task, where other tasks could get run inbetween)
- restarting the PWM if it was running before

Change-Id: Iebddc898c467c11dd412f239a8e26dd22f42c28b
int_sqrt.c: Correction square root algo with naming
int_sqrt: Improve 3x faster integer sqrt.

Result on 10,000,000 call.
Old:
sqrt(12345689) = 3513
real	0m0.768s
user	0m0.760s
sys	0m0.004s

New:
sqrt(12345689) = 3513
real	0m0.222s
user	0m0.224s
sys	0m0.000s