sunxi: Enable PMIC drivevbus regulator support for USB supplies

sunxi: Enable PMIC drivevbus regulator support for USB supplies

On many boards, the USB ports are powered by the PMIC's "drivevbus"
regulator. In preparation for switching the USB PHY driver to use the
regulator uclass instead of a virtual GPIO pin, ensure these boards
have AXP PMIC regulator support enabled.

Signed-off-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Jernej Skrabec <jernej.skrabec@gmail.com>