The X-Powers AXP323 is very close sibling to the AXP313A, only that it
adds support for dual-phasing the first two DC/DC converters.
We do not really care about this particular feature, so just add the new
compatible string and tie it to the existing AXP313A support code.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>