pwm: rockchip: Add a PWM driver for Rockchip SoCs

Add a simple driver which implements the standard PWM uclass interface.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
index d1b15e5..b6d8c16 100644
--- a/drivers/pwm/Makefile
+++ b/drivers/pwm/Makefile
@@ -11,4 +11,5 @@
 #ccflags-y += -DDEBUG
 
 obj-$(CONFIG_DM_PWM) += pwm-uclass.o
+obj-$(CONFIG_PWM_ROCKCHIP) += rk_pwm.o
 obj-$(CONFIG_PWM_IMX) += pwm-imx.o pwm-imx-util.o