msm: kgsl: Do direct register writes for A6XX perfcounter enable

For A6XX, use the path that goes directly to the register rather than
submitting the perfcounter enables through a ringbuffer submission.

Change-Id: I7b05c144fab534301ebdd51ea41a122bd740c0ac
Signed-off-by: Carter Cooper <ccooper@codeaurora.org>