qpnp: pwm: Add Keypad Backlight Lookup Table support

The Keypad Backlight Lookup Table (KPDBL_LUT) is similar to
a generic LUT found in PM8941 pmic with a minor differences such
as 8 bit LUT entry, and less LUT entries than generic LUT. Add
support for KPDBL_LUT to the PWM driver.

CRs-Fixed: 503480, 505751
Change-Id: Ice7b18e4b7681480e07bf25f4c258cfcbe58cb4d
Signed-off-by: Jay Chokshi <jchokshi@codeaurora.org>
Signed-off-by: Prasad Sodagudi <psodagud@codeaurora.org>