qpnp: pwm: Add support for GPLED LPG channels

The GPLED LPG channels are special case where in order to
use PWM mode, the ramp generator is also needs be enabled
according to hardware guidance. Add support for these channels
in the driver.

Change-Id: I6e132d083829a4ce0529de1070df41136a2668da
Signed-off-by: Jay Chokshi <jchokshi@codeaurora.org>