MAINTAINERS: Add dri-devel for backlight subsystem patches

MAINTAINERS: Add dri-devel for backlight subsystem patches

For the same reasons we've added dri-devel for all fbdev patches: Most
of the actively developed drivers using this infrastructure are in
drivers/gpu/. It just makes sense to cross-post patches and keep
aligned. And total activity in the backlight subsystem is miniscule
compared to drm overall.

Signed-off-by: Daniel Vetter <[email protected]>
Acked-by: Daniel Thompson <[email protected]>
Acked-by: Jingoo Han <[email protected]>
Reviewed-by: Jani Nikula <[email protected]>
Signed-off-by: Lee Jones <[email protected]>