drm/udl: Replace fbdev code with generic emulation

The udl driver can use the generic fbdev implementation. Convert it.

v5:
	* initialize console after registering device
v4:
	* hardcode console bpp to 16
v3:
	* remove module parameter fb_bpp in favor of fbdev's video
	* call drm_fbdev_generic_setup() directly; remove udl_fbdev_init()
	* use default for struct drm_mode_config_funcs.output_poll_changed
	* use default for struct drm_driver.lastclose

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Noralf Trønnes <noralf@tronnes.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191114125106.28347-2-tzimmermann@suse.de