msm: rpm-regulator: Add sleep-set force mode parameter

Add a new sleep_set_force_mode parameter into the rpm-regulator
driver platform data structure. Modify sleep-set requests to use
this value for force mode.

This parameter is intended to be used to capture platform
specific mode requirements for certain regulators which cannot
be managed by modifying peak current (ip) alone.

Change-Id: I7f25e546ae7feef1b5e8312a4198e855312a58c7
Signed-off-by: David Collins <collinsd@codeaurora.org>