mfd: lpc_ich: Add support for SPI serial flash host controller

Many Intel CPUs including Haswell, Broadwell and Baytrail have SPI serial
flash host controller as part of the LPC device. This will populate an MFD
cell suitable for the SPI host controller driver if we know that the LPC
device has one.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>