Add Keystone platform USB PHY driver support. Current main purpose
of this driver is to enable the PHY reference clock gate on the
Keystone SoC. Otherwise it is a nop PHY.

[ balbi@ti.com : add COMPILE_TEST as a possible dependency
	make sure drvdata is initialized before adding PHY ]

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: NSantosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: NWingMan Kwok <w-kwok2@ti.com>
Signed-off-by: NFelipe Balbi <balbi@ti.com>