This patch rewrite driver code to be ready to add support for
MC13892 LEDs and probe from devicetree.

(cooloney@gmail.com: fix one coding style issue when apply this patch)
Signed-off-by: NAlexander Shiyan <shc_work@mail.ru>
Tested-by: NPhilippe Retornaz <philippe.retornaz@epfl.ch>
Signed-off-by: NBryan Wu <cooloney@gmail.com>