spi: Add Socionext F_OSPI SPI flash controller driver

Introduce Socionext F_OSPI controller driver. This controller is used to
communicate with slave devices such as SPI flash memories. It supports
4 slave devices and up to 8-bit wide bus, but supports master mode only.

This driver uses spi-mem framework for SPI flash memory access, and
can only operate indirect access mode and single data rate mode.

Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>
diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
index 64ceed1..cdd2304 100644
--- a/drivers/spi/Kconfig
+++ b/drivers/spi/Kconfig
@@ -461,6 +461,14 @@
 	 Enable Soft SPI driver. This driver is to use GPIO simulate
 	 the SPI protocol.
 
+config SPI_SN_F_OSPI
+	tristate "Socionext F_OSPI SPI flash controller"
+	depends on SPI_MEM
+	help
+	  This enables support for the Socionext F_OSPI controller
+	  for connecting an SPI flash memory over up to 8-bit wide bus.
+	  It supports indirect access mode only.
+
 config SPI_SUNXI
 	bool "Allwinner SoC SPI controllers"
 	default ARCH_SUNXI