pwm: pwm-qti-lpg: Add LUT mode to support modulated PWM output

LPG module supports outputting the pattern programmed in Look-up table
(LUT) in addition to supporting PWM output. Add support for configuring
LPG to operate in LUT mode and configure LUT patterns per LPG channel.

Change-Id: I6352af136c4916f8b6bc17f1b8374ce1d421c10b
Signed-off-by: Fenglin Wu <fenglinw@codeaurora.org>