arm64: defconfig: enable the Marvell 10G PHY as a module

The Marvell 10G PHY is present on mvebu platforms. Enable it as a module
so that the network works on these platforms.

Signed-off-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>