drm/i915: Use intel_plane_state in prepare and cleanup plane_fb

drm/i915: Use intel_plane_state in prepare and cleanup plane_fb

We need to look at the hw fb in the plane split, so replace all the places
that use drm_plane_state with intel_plane_state.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191004113514.17064-6-maarten.lankhorst@linux.intel.com
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
[mlankhorst: Fix line wraps (Matt Roper)]
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>