dm: pwm: Add a PWM uclass

Add a uclass that supports Pulse Width Modulation (PWM) devices. It
provides methods to enable/disable and configure the device.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/dm/uclass-id.h b/include/dm/uclass-id.h
index b5f43ae..8f0381d 100644
--- a/include/dm/uclass-id.h
+++ b/include/dm/uclass-id.h
@@ -51,6 +51,7 @@
 	UCLASS_PINCTRL,		/* Pinctrl (pin muxing/configuration) device */
 	UCLASS_PINCONFIG,	/* Pin configuration node device */
 	UCLASS_PMIC,		/* PMIC I/O device */
+	UCLASS_PWM,		/* Pulse-width modulator */
 	UCLASS_PWRSEQ,		/* Power sequence device */
 	UCLASS_REGULATOR,	/* Regulator device */
 	UCLASS_RESET,		/* Reset device */