Backlight support should be implemented by panels, not by the LCDC
driver.  As the feature is currently unused anyway, remove it.
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
[geert: Cleanups]
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/69707650245bc2193d072f24723d4d5482ea590b.1694767209.git.geert+renesas@glider.be