msm: kgsl: Mark A4XX PWR and VBIF_PWR counter groups as fixed

As A3XX mark the A4XX PWR and VBIF_PWR performance counter groups
as fixed and simplify the macros as much as possible.

Change-Id: Ic0dedbade78ab7007f07db0148ada7e6effc7dce
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>