Memory-mapped dw_spi driver

Adds a memory-mapped I/O dw_spi platform device.

Signed-off-by: Jean-Hugues Deschenes <jean-hugues.deschenes@octasic.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

diff --cc drivers/spi/Kconfig
Simple merge

diff --cc drivers/spi/Makefile
Simple merge

diff --cc drivers/spi/dw_spi_mmio.c
Simple merge