bus: ti: am33xx: add pwm subsystem driver

The TI PWMSS driver is a simple bus driver for providing clock and power
management for the PWM peripherals on TI AM33xx SoCs, namely eCAP,
eHRPWM and eQEP.

For DT binding details see Linux doc:
- Documentation/devicetree/bindings/pwm/pwm-tipwmss.txt

Signed-off-by: Dario Binacchi <dariobin@libero.it>
diff --git a/drivers/bus/Kconfig b/drivers/bus/Kconfig
index 733bec5..d742ed3 100644
--- a/drivers/bus/Kconfig
+++ b/drivers/bus/Kconfig
@@ -5,6 +5,12 @@
 
 menu "Bus devices"
 
+config TI_PWMSS
+	bool
+	default y if ARCH_OMAP2PLUS && PWM_TI_EHRPWM
+	help
+	  PWM Subsystem driver support for AM33xx SOC.
+
 config TI_SYSC
 	bool "TI sysc interconnect target module driver"
 	depends on ARCH_OMAP2PLUS