arm64: dts: renesas: r8a77995: draak: Set better backlight levels

The backlight levels provided in the Draak DT produce a perceived
brightness very biased towards high brightness. Use better brightness
levels based on the CIE 1931 formula.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Ulrich Hecht <uli+renesas@fpond.eu>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>