drm/msm/gpu: add ocmem init/cleanup functions

The files a3xx_gpu.c and a4xx_gpu.c have ifdefs for the OCMEM support
that was missing upstream. Add two new functions (adreno_gpu_ocmem_init
and adreno_gpu_ocmem_cleanup) that removes some duplicated code.

Signed-off-by: Brian Masney <masneyb@onstation.org>
Reviewed-by: Jordan Crouse <jcrouse@codeaurora.org>
Tested-by: Gabriel Francisco <frc.gabrielgmail.com>
Signed-off-by: Rob Clark <robdclark@chromium.org>