drm/msm: Re-order uninit function to work during probe defer

If bind fails, we can call msm_drm_uninit before kms elements have been
created. In this case, drm_atomic_helper_shutdown will fail since there
are no drm objects. Only call drm unregistration and shutdown if drm is
registered.

Also while we're in here move the workqueue destruction to below
component_unbind since components could be actively using the wq during
uninit or in their unbind routine.

Reviewed-by: Rob Clark <robdclark@chromium.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190524202919.179289-1-sean@poorly.run