sunxi: Switch to PMIC USB power supply VBUS detection

Update boards to use the USB power supply driver, as referenced in the
device tree, instead of a virtual GPIO. This removes the need for some
DM-incompatible special cases in the GPIO driver.

The following five boards used AXP0-VBUS-DETECT in their config, but are
missing the "usb0_vbus_power-supply" property in their device tree:
 - Ainol_AW1_defconfig / sun7i-a20-ainol-aw1
 - Cubieboard4_defconfig / sun9i-a80-cubieboard4
 - Merrii_A80_Optimus_defconfig / sun9i-a80-optimus
 - Yones_Toptech_BD1078_defconfig / sun7i-a20-yones-toptech-bd1078
 - Yones_Toptech_BS1078_V2_defconfig /
   sun6i-a31s-yones-toptech-bs1078-v2

None of those five boards have the MUSB controller (USB OTG) enabled in
their device trees, so this change should not break anything for them.

Additionally, the following board intentionally omits the property
because VBUS is always enabled:
 - Nintendo_NES_Classic_Edition_defconfig /
   sun8i-r16-nintendo-nes-classic

The PHY driver already assumes VBUS is enabled when no detection method
is available, so again this will not cause any problems.

Signed-off-by: Samuel Holland <samuel@sholland.org>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>