Update the driver to initialize struct fb_info.bl_dev to its backlight
device, if any. Thus rely on the backlight core code to match backlight
and framebuffer devices, and remove the extra check_fb function from
struct backlight_ops.

v2:
	* protect against CONFIG_FB_BACKLIGHT (Javier, kernel test robot)
	* reword commit message (Daniel)
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Bruno Prémont <bonbons@linux-vserver.org>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://lore.kernel.org/r/20240305162425.23845-5-tzimmermann@suse.deSigned-off-by: Lee Jones <lee@kernel.org>