x86: Add SD/MMC support to quark/galileo

Intel Galileo board has a microSD slot which is routed from Quark SoC
SDIO controller. Enable SD/MMC support so that we can use an SD card.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>