sunxi: allow to use AXP20[39] attached to I2C0 on V3 series

The reference design of Allwinner V3 series uses an
AXP203 or AXP209 PMIC attached to the I2C0 bus of the SoC, although the
first community-available V3s board, Lichee Pi Zero, omitted it.

Allow to introduce support for the PMIC on boards with it.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>