sunxi: set PIO voltage to hardware-detected value on startup on H6

The Allwinner H6 SoC has a register to set the PIO banks' voltage. When
it mismatches the real voltage supplied to the VCC to the PIO supply,
the PIO will work improperly.

The PIO controller also has a register that contains the status of each
VCC rail of the PIO supplies, and it has the same definition with the
configuration register. so we can just copy the content of this register
to the configuration register at startup, to ensure the configuration is
correct at startup stage.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
[jagan: s/__maybe__unused/__maybe_unused]
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Acked-by: Jagan Teki <jagan@amarulasolutions.com>