drm: fix possible_crtc's type

drm_universal_plane_init() and drm_plane_init() take "unsigned long
possible_crtcs" parameter, but then stuff it into uint32_t. Change the
parameter to uint32_t.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>