sunxi: axp221: Make dcdc1 voltage configurable

The dcdc1 voltage is typically used as generic 3.3V IO voltage for things like
GPIO-s, sdcard interfaces, etc. On most boards this is undervolted to 3.0V to
safe battery, but not on all, make it configurable so that we can use the
same settings as the original firmware on all boards.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>