drm: omapdrm: Use kernel integer types

The standard kernel integer types are [us]{8,16,32}. Use them instead of
the u?int{8,16,32}_t types.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>