msm: kgsl: Consolidate regulator calls

Create a struct kgsl_regulator and use it to store regulator
pointer/name pairs and conslidate the bits that allocate and
use regulators.

Change-Id: Ic0dedbad8fb104e30038cbdb35aa74ce9b0817e9
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>