sunxi: Add support for AXP305 PMIC

This PMIC can be found on H616 boards and it's very similar to AXP805
and AXP806.

Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>