msm: kgsl: Use bulk clock functions for GMU

Instead of using a bespoke function to get the list of clocks, use the
built in functions instead. To do this, we'll need a local function
to get a clock pointer by name from the list so this is a great time to
add a file just for general purpose driver functions.

Change-Id: Ic0dedbad96f478afc1a416a94df7c0e203ecca8a
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>