msm: kgsl: Try to improve coresight register accesses

Instead of having if / else statements scattered throughout the
coresight driver to access GX or CX register banks use function
hooks in the target specific coresight structs. This helps
streamline the code and cut down on the decision points at the
cost of just a bit more infrastructure on the target side.

Change-Id: Ic0dedbada9d1632d220d0dfb186ccd0adff6be91
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>