drm/msm/adreno: split a6xx fault handler into generic and a6xx parts

Split the a6xx_fault_handler() into the generic adreno_fault_handler()
and platform-specific parts. The adreno_fault_handler() can further be
used by a5xx and hopefully by a4xx (at some point).

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/522722/
Link: https://lore.kernel.org/r/20230214123504.3729522-3-dmitry.baryshkov@linaro.org
Signed-off-by: Rob Clark <robdclark@chromium.org>