msm: kgsl: Move some helper functions out of gmu

Some of the gmu functions have common functionality
across A6xx GPUs. Move out these helper function from
gmu so that it can be reusable.

Change-Id: Idf623544854329a27ecbe52f28bbd2e90941fcba
Signed-off-by: Hareesh Gundu <hareeshg@codeaurora.org>