phy: sun4i-usb: add support for R40 USB PHY

Allwinner R40 features a USB PHY like the one in A64, but with 3 PHYs.

Add support for it.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Rob Herring <robh@kernel.org>
Tested-by: Hermann Lauer <Hermann.Lauer@iwr.uni-heidelberg.de>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>