Add delay between consecutive led brightness changes

Writing to brightness sysfs file triggers delayed activity in
the kernel side. Writing another value before the delayed
activity is finished can cause unexpected results.

Because there is no way to know when kernel side is finished,
a timer based state machine is used to ensure there is at least
10ms delay between the writes.

[hybris.so] Add delay between consecutive led brightness changes
Merge pull request #8 from spiiroin/led_control

Add delay between consecutive led brightness changes