drm/msm/a6xx: Mostly implement A7xx gpu_state

Provide the necessary alternations to mostly support state dumping on
A7xx. Newer GPUs will probably require more changes here. Crashdumper
and debugbus remain untested.

Tested-by: Neil Armstrong <neil.armstrong@linaro.org> # on SM8550-QRD
Tested-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org> # sm8450
Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/559289/
Signed-off-by: Rob Clark <robdclark@chromium.org>