backlight: add driver for DA9052/53 PMIC v1

DA9052/53 PMIC has capability to supply power for upto 3 banks of 6
white serial LEDS.  It can also control intensity of independent banks
and to drive these banks boost converter will provide up to 24V and
forward current of max 50mA.

This patch allows to control intensity of the individual WLEDs bank
through DA9052/53 PMIC.

This patch is functionally tested on Samsung SMDKV6410.

Signed-off-by: David Dajun Chen <dchen@diasemi.com>
Signed-off-by: Ashish Jangam <ashish.jangam@kpitcummins.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Cc: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>