Splitting plane state is easier than splitting crtc_state,
before plane check we copy the drm properties to hw so we can
do the same in bigjoiner later on.

We copy the state after we did all the modeset handling, but fortunately
i915 seems to be split correctly and nothing during modeset looks
at plane_state.

Changes since v1:
- Do not clear hw state on duplication.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191031112610.27608-11-maarten.lankhorst@linux.intel.com