drm/cirrus: Run DRM default client setup

drm/cirrus: Run DRM default client setup

Call drm_client_setup() 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.

The cirrus driver requests the same client pixel format as the value
stored in struct drm_mode_config.preferred_depth. The fbdev client
also looks at this value for the default pixel format. Thus remove
the format selection from cirrus.

v5:
- select DRM_CLIENT_SELECTION

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240924071734.98201-53-tzimmermann@suse.de