ARM: psci: add devicetree binding for describing PSCI firmware

This patch adds a new devicetree binding for describing PSCI firmware
to Linux.
Acked-by: NArnd Bergmann <arnd@arndb.de>
Acked-by: NNicolas Pitre <nico@linaro.org>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

Documentation/devicetree/bindings/arm/psci.txt

+* Power State Coordination Interface (PSCI)
+
+Firmware implementing the PSCI functions described in ARM document number
+ARM DEN 0022A ("Power State Coordination Interface System Software on ARM
+processors") can be used by Linux to initiate various CPU-centric power
+operations.
+
+Issue A of the specification describes functions for CPU suspend, hotplug
+and migration of secure software.
+
+Functions are invoked by trapping to the privilege level of the PSCI
+firmware (specified as part of the binding below) and passing arguments
+in a manner similar to that specified by AAPCS:
+
+	 r0		=> 32-bit Function ID / return value
+	{r1 - r3}	=> Parameters
+
+Note that the immediate field of the trapping instruction must be set
+to #0.
+
+
+Main node required properties:
+
+ - compatible    : Must be "arm,psci"
+
+ - method        : The method of calling the PSCI firmware. Permitted
+                   values are:
+
+                   "smc" : SMC #0, with the register assignments specified
+		           in this binding.
+
+                   "hvc" : HVC #0, with the register assignments specified
+		           in this binding.
+
+Main node optional properties:
+
+ - cpu_suspend   : Function ID for CPU_SUSPEND operation
+
+ - cpu_off       : Function ID for CPU_OFF operation
+
+ - cpu_on        : Function ID for CPU_ON operation
+
+ - migrate       : Function ID for MIGRATE operation
+
+
+Example:
+
+	psci {
+		compatible	= "arm,psci";
+		method		= "smc";
+		cpu_suspend	= <0x95c10000>;
+		cpu_off		= <0x95c10001>;
+		cpu_on		= <0x95c10002>;
+		migrate		= <0x95c10003>;
+	};