platform: msm: Add qpnp-pwm driver

Add the qpnp-pwm driver to support LPG/PWM devices in Qualcomm
plug-and-play (QPNP) PMIC chips.  QPNP chips make use of
Qualcomm's SPMI register convention. LPG module provides a superset
of functionality provided by PWM device such as user defined pattern
generation, driving multiple PWM channels etc.

Change-Id: I29a22c6e655612d93cac10e6eea76383d37775e2
Signed-off-by: Jay Chokshi <jchokshi@codeaurora.org>