cmd: Add a pwm command

Add the command "pwm" for controlling the pwm channels. This
command provides pwm invert/config/enable/disable functionalities
via PWM uclass drivers

Signed-off-by: Pragnesh Patel <pragnesh.patel@sifive.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/cmd/Makefile b/cmd/Makefile
index 87aa949..176bf92 100644
--- a/cmd/Makefile
+++ b/cmd/Makefile
@@ -120,6 +120,7 @@
 obj-$(CONFIG_CMD_PINMUX) += pinmux.o
 obj-$(CONFIG_CMD_PMC) += pmc.o
 obj-$(CONFIG_CMD_PSTORE) += pstore.o
+obj-$(CONFIG_CMD_PWM) += pwm.o
 obj-$(CONFIG_CMD_PXE) += pxe.o pxe_utils.o
 obj-$(CONFIG_CMD_WOL) += wol.o
 obj-$(CONFIG_CMD_QFW) += qfw.o