msm: kgsl: Remove the GMU power performance counters

Right now the GMU power perf counters are unused and we are out of
register address protection spans to make them available on older
targets.  Remove them now with an eye to returning them in the
future for newer targets that will have more protection spans to
work with.

Change-Id: Ic0dedbad69faa5e270265f14fb0206a3f0d82e25
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>