usb: musb: dsps: init / shutdown the phy

If the init / shutdown function of the phy moves out of dsps into the
phy driver, then dsps needs to call the callbacks of the phy driver to
ensure that this happens.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>