x86: galileo: Add GPIO support

Quark SoC has a legacy GPIO block in the legacy bridge (D0:F31),
which is just the same one found in other x86 chipset. Since we
programmed the GPIO register block base address, we should be
able to enable the GPIO support on Intel Galileo board.

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