Documentation: devicetree: Document BCM23550 bindings

Add binding document for Broadcom BCM23550 SoC.

BCM23550 has a Cluster Dormant Control IP block that holds cores
in an idle state. Introduce a new CPU enable method in which the CDC is
accessed to bring the core online.
Signed-off-by: Chris Brand <chris.brand@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

Documentation/devicetree/bindings/arm/bcm/brcm,bcm23550-cpu-method.txt

+Broadcom Kona Family CPU Enable Method
+--------------------------------------
+This binding defines the enable method used for starting secondary
+CPUs in the following Broadcom SoCs:
+  BCM23550
+
+The enable method is specified by defining the following required
+properties in the "cpu" device tree node:
+  - enable-method = "brcm,bcm23550";
+  - secondary-boot-reg = <...>;
+
+The secondary-boot-reg property is a u32 value that specifies the
+physical address of the register used to request the ROM holding pen
+code release a secondary CPU.  The value written to the register is
+formed by encoding the target CPU id into the low bits of the
+physical start address it should jump to.
+
+Example:
+	cpus {
+		#address-cells = <1>;
+		#size-cells = <0>;
+
+		cpu0: cpu@0 {
+			device_type = "cpu";
+			compatible = "arm,cortex-a9";
+			reg = <0>;
+		};
+
+		cpu1: cpu@1 {
+			device_type = "cpu";
+			compatible = "arm,cortex-a9";
+			reg = <1>;
+			enable-method = "brcm,bcm23550";
+			secondary-boot-reg = <0x3500417c>;
+		};
+	};

Documentation/devicetree/bindings/arm/bcm/brcm,bcm23550.txt

+Broadcom BCM23550 device tree bindings
+--------------------------------------
+
+This document describes the device tree bindings for boards with the BCM23550
+SoC.
+
+Required root node property:
+  - compatible: brcm,bcm23550
+
+Example:
+	/ {
+		model = "BCM23550 SoC";
+		compatible = "brcm,bcm23550";
+		[...]
+	}

Documentation/devicetree/bindings/arm/cpus.txt

@@ -194,6 +194,7 @@ nodes to be present and contain the properties described below.
 			    "allwinner,sun8i-a23"
 			    "arm,realview-smp"
 			    "brcm,bcm11351-cpu-method"
+			    "brcm,bcm23550"
 			    "brcm,bcm-nsp-smp"
 			    "brcm,brahma-b15"
 			    "marvell,armada-375-smp"