arm64: dts: renesas: r8a77990: ebisu: Enable EthernetAVB

This patch enables EthernetAVB for r8a77990 Ebisu board.

Based on a patch from Takeshi Kihara <takeshi.kihara.df@renesas.com>

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>