PWMLED: proof-of-concept brightness setting

In order to save space for patterns, we set the brightness
independently from pattern. Each brightness has only two levels
for PWMLED 0 and 2, and one for PWMLED 1. Patterns can then use
two-bit values for each PWMLED (one-bit for PWMLED 1), with the
following meaning:

0: off
1: level 1
2: level 2
3: also level 2, with a separate state stored. This can be used for
	saving regulation value for a single current level with
	and without other outputs running, or with different levels
	of other output. This is in order to avoid flicker when one
	PWMLED (usually the front one) is steady on, and the others
	are blinking.