drm/fbdev-dma: Remove obsolete setup function

The old setup function drm_fbdev_dma_setup() is unused. Remove it and
its internal callbacks. New drivers should call drm_client_setup()
instead.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240924071734.98201-49-tzimmermann@suse.de