drm: Make ioctls available for in-kernel clients

Make ioctl wrappers for functions that will be used by the in-kernel API.
The following functions are touched:
- drm_mode_create_dumb_ioctl()
- drm_mode_destroy_dumb_ioctl()
- drm_mode_addfb()
- drm_mode_rmfb()

Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20180618141739.48151-4-noralf@tronnes.org