usb: musb: dsps: remove the hardcoded phy pieces

dsps uses a nop driver which is added in dsps itself and does the PHY
on/off calls within dsps. Since those calls are now moved the nop driver
itself, we can now request the phy proper phy and remove those calls.
Currently only the first musb interface is used so we only add one phy
node for now.

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