arm64: dts: renesas: r8a77990: ebisu: Enable VGA and HDMI outputs

Add the LVDS decoder, HDMI encoder, VGA encoder and HDMI and VGA
connectors, and wire up the display-related nodes with clocks, pinmux
and regulators.

The LVDS0 and LVDS1 encoders can use the DU_DOTCLKIN0, DU_DOTCLKIN1 and
EXTAL externals clocks. Two of them are provided to the SoC on the Ebisu
board, hook them up in DT.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Tested-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>