arm64: defconfig: enable EthernetAVB

This is present on the Renesas r8a7795 SoC and may be
used by the Salvator-X board.

Also enable MICREL_PHY which is used on the Salvator-X board.

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>