Initialize i915's fbdev client by giving an instance of struct
drm_client_funcs to drm_client_init(). Also clean up with
drm_client_release().

Doing this in i915 prevents fbdev helpers from initializing and
releasing the client internally (see drm_fb_helper_init()). No
functional change yet; the client callbacks will be filled later.

v6:
- rename client to "intel-fbdev" (Jouni)

v2:
- call drm_fb_helper_unprepare() in error handling (Jani)
- fix typo in commit message (Sam)
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/20240409081029.17843-4-tzimmermann@suse.deSigned-off-by: Jani Nikula <jani.nikula@intel.com>