Documentation: Add documentation for the APM X-Gene SoC SATA host controller DTS binding

This patch adds documentation for the APM X-Gene SoC SATA host controller DTS
binding.
Signed-off-by: Loc Ho <lho@apm.com>
Signed-off-by: Tuan Phan <tphan@apm.com>
Signed-off-by: Suman Tripathi <stripathi@apm.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Tejun Heo <tj@kernel.org>

Documentation/devicetree/bindings/ata/apm-xgene.txt

+* APM X-Gene 6.0 Gb/s SATA host controller nodes
+
+SATA host controller nodes are defined to describe on-chip Serial ATA
+controllers. Each SATA controller (pair of ports) have its own node.
+
+Required properties:
+- compatible		: Shall contain:
+  * "apm,xgene-ahci"
+- reg			: First memory resource shall be the AHCI memory
+			  resource.
+			  Second memory resource shall be the host controller
+			  core memory resource.
+			  Third memory resource shall be the host controller
+			  diagnostic memory resource.
+			  4th memory resource shall be the host controller
+			  AXI memory resource.
+			  5th optional memory resource shall be the host
+			  controller MUX memory resource if required.
+- interrupts		: Interrupt-specifier for SATA host controller IRQ.
+- clocks		: Reference to the clock entry.
+- phys			: A list of phandles + phy-specifiers, one for each
+			  entry in phy-names.
+- phy-names		: Should contain:
+  * "sata-phy" for the SATA 6.0Gbps PHY
+
+Optional properties:
+- status		: Shall be "ok" if enabled or "disabled" if disabled.
+			  Default is "ok".
+
+Example:
+		sataclk: sataclk {
+			compatible = "fixed-clock";
+			#clock-cells = <1>;
+			clock-frequency = <100000000>;
+			clock-output-names = "sataclk";
+		};
+
+		phy2: phy@1f22a000 {
+			compatible = "apm,xgene-phy";
+			reg = <0x0 0x1f22a000 0x0 0x100>;
+			#phy-cells = <1>;
+		};
+
+		phy3: phy@1f23a000 {
+			compatible = "apm,xgene-phy";
+			reg = <0x0 0x1f23a000 0x0 0x100>;
+			#phy-cells = <1>;
+		};
+
+		sata2: sata@1a400000 {
+			compatible = "apm,xgene-ahci";
+			reg = <0x0 0x1a400000 0x0 0x1000>,
+			      <0x0 0x1f220000 0x0 0x1000>,
+			      <0x0 0x1f22d000 0x0 0x1000>,
+			      <0x0 0x1f22e000 0x0 0x1000>,
+			      <0x0 0x1f227000 0x0 0x1000>;
+			interrupts = <0x0 0x87 0x4>;
+			status = "ok";
+			clocks = <&sataclk 0>;
+			phys = <&phy2 0>;
+			phy-names = "sata-phy";
+		};
+
+		sata3: sata@1a800000 {
+			compatible = "apm,xgene-ahci-pcie";
+			reg = <0x0 0x1a800000 0x0 0x1000>,
+			      <0x0 0x1f230000 0x0 0x1000>,
+			      <0x0 0x1f23d000 0x0 0x1000>,
+			      <0x0 0x1f23e000 0x0 0x1000>,
+			      <0x0 0x1f237000 0x0 0x1000>;
+			interrupts = <0x0 0x88 0x4>;
+			status = "ok";
+			clocks = <&sataclk 0>;
+			phys = <&phy3 0>;
+			phy-names = "sata-phy";
+		};