Device nodes representing I/O devices should be marked disabled in the
SoC-specific DTS, and overridden by board-specific DTSes where needed.

Fixes: 8e8b9eae ("arm64: dts: renesas: r8a7796: Add EthernetAVB instance")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>