usb: phy: Add driver for the Ingenic JZ4770 USB transceiver

Add a driver to support the USB PHY found in the JZ4770 SoC from
Ingenic.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lore.kernel.org/r/20200229161820.17824-2-paul@crapouillou.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>