Remove all hooks and calls into code for user-space mode setting from
the DRM core. Without the drivers and ioctl entry points, none of this
is required any longer.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: David Airlie <airlied@gmail.com>
Reviewed-by: Daniel Vetter <daniel@ffwll.ch>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231122122449.11588-11-tzimmermann@suse.de