Add SPI flash driver

This driver is taken from u-boot and adapted to match
coreboot. It still contains some hacks and is ICH specific
at places.

Change-Id: I97dd8096f7db3b62f8f4f4e4d08bdee10d88f689
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/997
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
diff --git a/src/drivers/Makefile.inc b/src/drivers/Makefile.inc
index 5f6dadf..851a4df 100644
--- a/src/drivers/Makefile.inc
+++ b/src/drivers/Makefile.inc
@@ -26,4 +26,5 @@
 subdirs-y += sil
 subdirs-y += trident
 subdirs-y += ics
+subdirs-y += spi
 subdirs-$(CONFIG_ARCH_X86) += pc80