pwm: Add CLPS711X PWM support

Add a new driver for the ARM CLPS711X Pulse Width Modulator (PWM) interface.
This CPU contain two 4-bit PWM outputs with constant period, based on CPU
PLL frequency. PWM polarity is determined by hardware by power on reset.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

Documentation/devicetree/bindings/pwm/cirrus,clps711x-pwm.txt

@@ -0,0 +1,16 @@
+* Cirris Logic CLPS711X PWM controller
+
+Required properties:
+- compatible: Shall contain "cirrus,clps711x-pwm".
+- reg: Physical base address and length of the controller's registers.
+- clocks: phandle + clock specifier pair of the PWM reference clock.
+- #pwm-cells: Should be 1. The cell specifies the index of the channel.
+
+Example:
+	pwm: pwm@80000400 {
+		compatible = "cirrus,ep7312-pwm",
+			     "cirrus,clps711x-pwm";
+		reg = <0x80000400 0x4>;
+		clocks = <&clks 8>;
+		#pwm-cells = <1>;
+	};