What:		/sys/bus/platform/devices/ci_hdrc.0/role
Date:		Mar 2017
Contact:	Peter Chen <peter.chen@nxp.com>
Description:
		When read, it returns string "gadget" or "host", indicating
		the current controller role.

		It will do role switch when "gadget" or "host" is written to it.
		Only controller at dual-role configuration supports writing.
