drm/atmel: Drop transitional hooks

These do absolutely nothing for atomic drivers.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Boris Brezillon <boris.brezillon@bootlin.com>
Cc: Nicolas Ferre <nicolas.ferre@microchip.com>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: linux-arm-kernel@lists.infradead.org
Link: https://patchwork.freedesktop.org/patch/msgid/20181004202446.22905-10-daniel.vetter@ffwll.ch