dt: bindings: add pmu0 regs for USB PHYs on Allwinner H3/V3s/A64

Allwinner H3/V3s/A64 SoCs have a special USB PHY0 that can route to two
controllers: one is MUSB and the other is a EHCI/OHCI pair.

When it's routed to EHCI/OHCI pair, it will needs a "pmu0" regs to
tweak, like other EHCI/OHCI pairs in Allwinner SoCs.

Add this to the binding of USB PHYs on Allwinner H3/V3s/A64.

Signed-off-by: Icenowy Zheng <icenowy@aosc.xyz>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>