drm/msm/a6xx: Use the per-GPU value for gmu_cgc_mode

This register's magic value differs wildly between different GPUs, use
the hardcoded data instead of trying to make some logic out of it.

Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/611096/


Signed-off-by: Rob Clark <robdclark@chromium.org>