Always disable all LEDs before updating them.

This should make sure the PWMs for red/green/blue always run in sync,
not only when switching between the various light types
(attention/battery/notification).

Change-Id: I0d743f31b645445da04436fd8ab8e8fdec39dfb9
Clean up lights module code.

Change-Id: Ic195efafde9dba965727d055576df5f6b2a1431b