regulator: Add the MSM GFX LDO regulator driver

The GPU core on MSM TITANIUM can be powered by an internal
MSM (on-die) LDO or BHS. Typically the lower voltage corners
are powered by the LDO and the higher corners by BHS. Add
support to configure the LDO and hand-off between LDO and BHS.

Change-Id: Id13b6b601c91aa6c2c2f0e6d820a244144b60437
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>