leds: pmic8058: Add PMIC leds driver

Add PMIC8058 based keyboard backlight and low current leds driver.

keyboard backlight led supports upto 16 levels of backlight intensity,
which is mapped to 0..255 levels of brightness of led subsystem.

Three low current(40mA) led drivers of PMIC are also supported
in this driver.

CRs-Fixed: 211772
Change-Id: Ia65b083f6070666aaad95851c9b843332ce35c82
Signed-off-by: Trilok Soni <tsoni@qualcomm.com>