Unregister all in-kernel clients before unloading the i915 driver. For
other drivers, drm_dev_unregister() does this automatically. As i915 and
xe do not use this helper, they have to perform the call by themselves.

Note that there are currently no in-kernel clients in i915 or xe. The
patch prepares the drivers for a related update of their fbdev support.

v8:
- unregister clients in intel_display_driver_unregister() (Jani)
- mention xe in commit message (Rodrigo, Jani)

v7:
- update xe driver
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Acked-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240409081029.17843-5-tzimmermann@suse.deSigned-off-by: Jani Nikula <jani.nikula@intel.com>