sunxi: H616: remove default AXP305 selection

The original H616 devices released about three years ago were typically
paired with an X-Powers AXP305 PMIC. Newer devices uses the smaller
AXP313, and there seem to be far more systems with this PMIC around now.

Remove the default AXP305 selection for the H616 SoC from the Kconfig,
and move the PMIC selection into the board defconfig files instead.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>