drm/client: Add hotplug_failed flag

Signal failed hotplugging with a flag in struct drm_client_dev. If set,
the client helpers will not further try to set up the fbdev display.

This used to be signalled with a combination of cleared pointers in
struct drm_fb_helper, which prevents us from initializing these pointers
early after allocation.

The change also harmonizes behavior among DRM clients. Additional DRM
clients will now handle failed hotplugging like fbdev does.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230125200415.14123-3-tzimmermann@suse.de