pwm: qti-lpg: Adapt to two-nvmem PBS triggering scheme

PM8350C PWM PPG does away with the need to directly manage the PBS
triggering via the PBS driver APIs by using a single register write to
an SDAM register instead. A PBS sequence thus triggered should be duly
cleared before next use. The existing scheme is also retained for
backward compatibility with targets that use a single-nvmem scheme.

The new PBS triggering scheme also expects a change in the way the high
and low indices pertaining to the pattern are specified.

Change-Id: I7d07dc611f98ce32cf5e8ba7de758fbbc3513f4b
Signed-off-by: Guru Das Srinagesh <gurus@codeaurora.org>