Documentation: devicetree: add Broadcom SATA binding

Signed-off-by: NBrian Norris <computersforpeace@gmail.com>
Signed-off-by: NTejun Heo <tj@kernel.org>

Documentation/devicetree/bindings/ata/brcm,sata-brcmstb.txt

+* Broadcom SATA3 AHCI Controller for STB
+
+SATA nodes are defined to describe on-chip Serial ATA controllers.
+Each SATA controller should have its own node.
+
+Required properties:
+- compatible         : compatible list, may contain "brcm,bcm7445-ahci" and/or
+                       "brcm,sata3-ahci"
+- reg                : register mappings for AHCI and SATA_TOP_CTRL
+- reg-names          : "ahci" and "top-ctrl"
+- interrupts         : interrupt mapping for SATA IRQ
+
+Also see ahci-platform.txt.
+
+Example:
+
+	sata@f045a000 {
+		compatible = "brcm,bcm7445-ahci", "brcm,sata3-ahci";
+		reg = <0xf045a000 0xa9c>, <0xf0458040 0x24>;
+		reg-names = "ahci", "top-ctrl";
+		interrupts = <0 30 0>;
+		#address-cells = <1>;
+		#size-cells = <0>;
+
+		sata0: sata-port@0 {
+			reg = <0>;
+			phys = <&sata_phy 0>;
+		};
+
+		sata1: sata-port@1 {
+			reg = <1>;
+			phys = <&sata_phy 1>;
+		};
+	};