drm/msm/a6xx: Don't enable GPU state code if dependencies are missing

Add CONFIG_DRM_MSM_GPU_STATE to conditionally compile Adreno GPU state
code depending on the availability of the dependencies.

Reported-by: Hulk Robot <hulkci@huawei.com>
Reported-by: YueHaibing <yuehaibing@huawei.com>
Fixes: 1707add8 ("drm/msm/a6xx: Add a6xx gpu state")
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>