x86: spi: Add Intel ICH driver

This supports Intel ICH7/9. The Intel controller is a little unusual in
that it is mostly intended for use with SPI flash, and has some
optimisations and features specifically for that application. In
particular it is not possible to support ongoing transactions that
continue over many calls with SPI_XFER_BEGIN and SPI_XFER_END.

This driver supports writes of up to 64 bytes at a time, the limit
for the controller. Future work will improve this.

Signed-off-by: Bernie Thompson <bhthompson@chromium.org>
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Signed-off-by: Bill Richardson <wfrichar@chromium.org>
Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Signed-off-by: Gabe Black <gabeblack@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>