drm/msm: Stop consulting plane->fb/crtc

drm/msm: Stop consulting plane->fb/crtc

We want to get rid of plane->fb/crtc on atomic drivers. Stop
looking at them.

v2: Catch the plane->crtc case too

Cc: Rob Clark <robdclark@gmail.com>
Cc: linux-arm-msm@vger.kernel.org
Cc: freedreno@lists.freedesktop.org
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com> #v1
Link: https://patchwork.freedesktop.org/patch/msgid/20180405151400.11326-1-ville.syrjala@linux.intel.com
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>