usb: phy: am335x: add wakeup support

This is based on George Cherian's patch which added power & wakeup
support to am335x and does no longer apply since I took some if the code
apart in favor of the multi instance support.
This compiles and I boots and later it detects a device after I plug it in :)
Could somebody please test it so it does what it should?

Cc: George Cherian <george.cherian@ti.com>
Reviewed-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>