On the current structure HSW doesn't support PSR with sprites enabled
but sprites can be enabled after PSR was enabled what would cause
user to miss screen updates.

v2: move it to update_plane.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Vijay Purushothaman <vijay.a.purushothaman@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>