ARM: dts: imx6qdl-vicut1/vicutgo: Rename backlight to backlight_lcd

We have two backlight sources on this boards. Use more specific name for
the LCD backlight to see the difference.

Signed-off-by: David Jander <david@protonic.nl>
Signed-off-by: Robin van der Gracht <robin@protonic.nl>
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>