HID: thingm: add support for blink(1) mk2

The blink(1) mk2 is a new version of the blink(1) USB RGB LED. The new
generation has 2 individually-controllable RGB chips.

This patch adds support for this device to the thingm driver, which
registers 3 new standard LED class instances for the second RGB chip.

Note that the 'n' (set) command does not support setting a color for a
single RGB chip, so it was changed to 'c' (fade) with a timeout of 0.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>