x86: Add SPI support to quark/galileo

The Quark SoC contains a legacy SPI controller in the legacy bridge
which is ICH7 compatible. Like Tunnel Creek and BayTrail, the BIOS
control register offset in the ICH SPI driver is wrong for the Quark
SoC too, unprotect_spi_flash() is added to enable the flash write.

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