phy: sun50i-usb3: Add a driver for the H6 USB3 PHY

This driver is needed for XHCI to work on the Allwinner H6 SoC. The
driver is copied from Linux v5.10.

Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>