spi: Add driver for IMG SPFI controller

Add support for the Synchronous Peripheral Flash Interface (SPFI) master
controller found on IMG SoCs.  The SPFI controller supports 5 chip-select
lines and single/dual/quad mode SPI transfers.

Signed-off-by: Andrew Bresticker <abrestic@chromium.org>
Signed-off-by: Mark Brown <broonie@kernel.org>