usb: dwc3: pci: Enable ULPI Refclk on platforms where the firmware does not

On some Bay Trail (BYT) systems the firmware does not enable the
ULPI Refclk.

This commit adds a helper which checks and if necessary enabled the Refclk
and calls this helper for BYT machines.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>