drm: Stop updating plane->crtc/fb/old_fb on atomic drivers

drm: Stop updating plane->crtc/fb/old_fb on atomic drivers

Stop playing around with plane->crtc/fb/old_fb with atomic
drivers. Make life a lot simpler when we don't have to do the
magic old_fb vs. fb dance around plane updates. That way we
can't risk plane->fb getting out of sync with plane->state->fb
and we're less likely to leak any refcounts as well.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180525185045.29689-14-ville.syrjala@linux.intel.com
Reviewed-by: Sinclair Yeh <syeh@vmware.com>