usb: dwc3-otg: Register USB2 and USB3 PHYs for MSM

otg_get(put)_transceiver APIs have been removed and drivers are
now required to use usb_add_(remove)_phy APIs. Also, dwc3 core
driver fails initialization very early (during probe) if both
USB2 and USB3 PHYs are not present. This check happens before
dwc3 OTG driver gets a chance to run and add PHYs, hence, add
mechanism to allow dwc3-msm (aka ext_xcvr) driver to add USB2
and USB3 PHYs during probe by calling a new API exported by
dwc3_otg driver.

Signed-off-by: Manu Gautam <mgautam@codeaurora.org>