spi/topcliff: Add topcliff platform controller hub (PCH) spi bus driver

Topcliff PCH is the platform controller hub that is going to be used
in Intel's upcoming general embedded platform. All IO peripherals in
Topcliff PCH are actually devices sitting on AMBA bus.  This patch
adds a driver for the SPI bus integrated into the Topcliff device.

Signed-off-by: Masayuki Ohtake <masa-korg@dsn.okisemi.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>