drm/xlnx: Run DRM default client setup

Call drm_client_setup_with_fourcc() to run the kernel's default client
setup for DRM. Set fbdev_probe in struct drm_driver, so that the client
setup can start the common fbdev client.

v5:
- select DRM_CLIENT_SELECTION
v2:
- use drm_client_setup_with_fourcc()

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Cc: Michal Simek <michal.simek@amd.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240924071734.98201-48-tzimmermann@suse.de