configs/vexpress64: add SATA_SIL24 and SKY2 configure for Juno PCIe

User can enable vexpress64.conf as following:

ARCH=arm64 scripts/kconfig/merge_config.sh arch/arm64/configs/defconfig \
linaro/configs/vexpress64.conf

Signed-off-by: Alex Shi <alex.shi@linaro.org>