fotg210-udc: Support optional external PHY

This adds support for an optional external PHY to the FOTG210
UDC driver.

Tested with the GPIO VBUS PHY driver on the Gemini SoC.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20221114115201.302887-2-linus.walleij@linaro.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>