dt-bindings: cpufreq: Add binding for NVIDIA Tegra20/30

Add device-tree binding that describes CPU frequency-scaling hardware
found on NVIDIA Tegra20/30 SoCs.
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Peter De Schrijver <pdeschrijver@nvidia.com>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>

Documentation/devicetree/bindings/cpufreq/nvidia,tegra20-cpufreq.txt

+Binding for NVIDIA Tegra20 CPUFreq
+==================================
+
+Required properties:
+- clocks: Must contain an entry for the CPU clock.
+  See ../clocks/clock-bindings.txt for details.
+- operating-points-v2: See ../bindings/opp/opp.txt for details.
+- #cooling-cells: Should be 2. See ../thermal/thermal.txt for details.
+
+For each opp entry in 'operating-points-v2' table:
+- opp-supported-hw: Two bitfields indicating:
+	On Tegra20:
+	1. CPU process ID mask
+	2. SoC speedo ID mask
+
+	On Tegra30:
+	1. CPU process ID mask
+	2. CPU speedo ID mask
+
+	A bitwise AND is performed against these values and if any bit
+	matches, the OPP gets enabled.
+
+- opp-microvolt: CPU voltage triplet.
+
+Optional properties:
+- cpu-supply: Phandle to the CPU power supply.
+
+Example:
+	regulators {
+		cpu_reg: regulator0 {
+			regulator-name = "vdd_cpu";
+		};
+	};
+
+	cpu0_opp_table: opp_table0 {
+		compatible = "operating-points-v2";
+
+		opp@456000000 {
+			clock-latency-ns = <125000>;
+			opp-microvolt = <825000 825000 1125000>;
+			opp-supported-hw = <0x03 0x0001>;
+			opp-hz = /bits/ 64 <456000000>;
+		};
+
+		...
+	};
+
+	cpus {
+		cpu@0 {
+			compatible = "arm,cortex-a9";
+			clocks = <&tegra_car TEGRA20_CLK_CCLK>;
+			operating-points-v2 = <&cpu0_opp_table>;
+			cpu-supply = <&cpu_reg>;
+			#cooling-cells = <2>;
+		};
+	};