usb: dwc2: gadget: Move gadget phy init into core phy init

Most of the phy initialization is shared between host and gadget,
this adds the turnaround configuration only used by gadgets to
the global phy init.

Acked-by: Minas Harutyunyan <hminas@synopsys.com>
Signed-off-by: Jules Maselbas <jmaselbas@kalray.eu>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>