arm64: allwinner: a64: add pmu0 regs for USB PHY

The USB PHY in A64 has a "pmu0" region, which controls the EHCI/OHCI
controller pair that can be connected to the PHY0.

Add the MMIO region for PHY node.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>