usb: phy: move bulk of otg/otg.c to phy/phy.c

Most of otg/otg.c is not otg specific, but phy specific, so move it
to the phy directory.

Tested-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
Reported-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>