arm64: configs: Enable X-Gene SATA and ethernet in defconfig

Currently when run on an APM platform the ARMv8 defconfig has no viable
options for rootfs other than ramdisk which is rather limiting. Since
we already have both SATA and the bits needed for NFS root enabled we just
need to enable the relevant drivers so do that, helping enable direct
testing of upstream.

If the configuration ends up becoming too big we can consider modularising
some of the drivers and asking people to use an initramfs but for now this
is not an issue.

Signed-off-by: Mark Brown <broonie@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>