drm/msm: Disable preemption on all 5xx targets

commit 7b3f3948c8b7053d771acc9f79810cc410f5e2e0 upstream.

Temporarily disable preemption on a5xx targets pending some improvements
to protect the RPTR shadow from being corrupted.

Cc: stable@vger.kernel.org
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>