arm64: dts: r8a7796: salvator-x: Enable EthernetAVB

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
[geert: Add pinctrl]
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>