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/doc/device-tree-bindings/spi/spi-ath79.txt b/doc/device-tree-bindings/spi/spi-ath79.txt
new file mode 100644
index 0000000..3fd9d67
--- /dev/null
+++ b/doc/device-tree-bindings/spi/spi-ath79.txt
@@ -0,0 +1,19 @@
+Binding for Qualcomm Atheros AR7xxx/AR9xxx SPI controller
+
+Required properties:
+- compatible: has to be "qca,<soc-type>-spi", "qca,ar7100-spi" as fallback.
+- reg: Base address and size of the controllers memory area
+- #address-cells: <1>, as required by generic SPI binding.
+- #size-cells: <0>, also as required by generic SPI binding.
+
+Child nodes as per the generic SPI binding.
+
+Example:
+
+	spi@1f000000 {
+		compatible = "qca,ar9132-spi", "qca,ar7100-spi";
+		reg = <0x1f000000 0x10>;
+
+		#address-cells = <1>;
+		#size-cells = <0>;
+	};