drm/rockchip: Use drm_plane_state.{src, dst}

Replace the private drm_rects in vop_plane_state with
the ones now living in drm_plane_state.

Cc: Yao <mark.yao@rock-chips.com>
Cc: linux-rockchip@lists.infradead.org
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Acked-by: Mark Yao <mark.yao@rock-chips.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1469549224-1860-7-git-send-email-ville.syrjala@linux.intel.com