pwm: Add PWM driver for HiSilicon BVT SOCs

Add PWM driver for the PWM controller found on HiSilicon BVT SoCs such
as Hi3519V100, Hi3516CV300, etc. The PWM controller is primarily in
charge of controlling the P-Iris lens.

Reviewed-by: Jiancheng Xue <xuejiancheng@hisilicon.com>
Signed-off-by: Jian Yuan <yuanjian12@hisilicon.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

Documentation/devicetree/bindings/pwm/pwm-hibvt.txt

@@ -0,0 +1,21 @@
+Hisilicon PWM controller
+
+Required properties:
+-compatible: should contain one SoC specific compatible string
+ The SoC specific strings supported including:
+	"hisilicon,hi3516cv300-pwm"
+	"hisilicon,hi3519v100-pwm"
+- reg: physical base address and length of the controller's registers.
+- clocks: phandle and clock specifier of the PWM reference clock.
+- resets: phandle and reset specifier for the PWM controller reset.
+- #pwm-cells: Should be 3. See pwm.txt in this directory for a description of
+  the cells format.
+
+Example:
+	pwm: pwm@12130000 {
+		compatible = "hisilicon,hi3516cv300-pwm";
+		reg = <0x12130000 0x10000>;
+		clocks = <&crg_ctrl HI3516CV300_PWM_CLK>;
+		resets = <&crg_ctrl 0x38 0>;
+		#pwm-cells = <3>;
+	};