drm/omap: add plane_atomic_print_state support

Now that we added specific item to our subclassed drm_plane_state
we can add omap_plane_atomic_print_state() helper to dump out our own
driver specific plane state.

Signed-off-by: Benoit Parrot <bparrot@ti.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211117141928.771082-9-narmstrong@baylibre.com