drivers: spi: add spi support for QCA/Atheros ath79 SOCs

This patch add a compatible spi driver for ath79 series SOC.

Signed-off-by: Wills Wang <wills.wang@live.com>
Reviewed-by: Thomas Chou <thomas@wytron.com.tw>
Reviewed-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
index f0258f8..b7fd8e5 100644
--- a/drivers/spi/Kconfig
+++ b/drivers/spi/Kconfig
@@ -23,6 +23,15 @@
 	  IP core. Please find details on the "Embedded Peripherals IP
 	  User Guide" of Altera.
 
+config ATH79_SPI
+	bool "Atheros SPI driver"
+	depends on ARCH_ATH79
+	help
+	  Enable the Atheros ar7xxx/ar9xxx SoC SPI driver, it was used
+	  to access SPI NOR flash and other SPI peripherals. This driver
+	  uses driver model and requires a device tree binding to operate.
+	  please refer to doc/device-tree-bindings/spi/spi-ath79.txt.
+
 config CADENCE_QSPI
 	bool "Cadence QSPI driver"
 	help