drm: Add GPU performance counter for DRM driver.

Ported performance counter changes from KGSL driver.
we can read all the GPU perf counter values in DRM based
GPU driver.

Change-Id: I4810de3b7232cbf5069645d8ff504d258c9eaa01
Signed-off-by: Kiran Sunilrao Khatke <c-kkhatk@codeaurora.org>
Signed-off-by: Bharathraj Nagaraju <snbraj@codeaurora.org>