usb: dwc2: pci: Select the generic PHY for dwc2-pci driver

The dwc2-pci driver requires the generic PHY. This fixes undefined
reference issues when it is not selected.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>