arm64: dts: allwinner: orange-pi-3: Enable WiFi

Orange Pi 3 has AP6256 WiFi/BT module. WiFi part of the module is called
bcm43356 and can be used with the brcmfmac driver. The module is powered by
the two always on regulators (not AXP805).

WiFi uses a PG port with 1.8V voltage level signals. SoC needs to be
configured so that it sets up an 1.8V input bias on this port. This is done
by the pio driver by reading the vcc-pg-supply voltage.

You'll need a fw_bcm43456c5_ag.bin firmware file and nvram.txt
configuration that can be found in the Xulongs's repository for H6:

https://github.com/orangepi-xunlong/OrangePiH6_external/tree/master/ap6256



Mainline brcmfmac driver expects the firmware and nvram at the following
paths relative to the firmware directory:

  brcm/brcmfmac43456-sdio.bin
  brcm/brcmfmac43456-sdio.txt

Signed-off-by: Ondrej Jirman <megous@megous.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>