sunxi: Olimex A20 boards: Enable LDO3 and LDO4 regulators

Sets LDO3 and LDO4 regulators at 2.8V. In the current config
these are off. This causes kernel to hang during
axp209 initialization.

Signed-off-by: Stefan Mavrodiev <stefan.mavrodiev@gmail.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>