ARM: dts: sun8i-v3: Add support for the SL631 Action Camera with IMX179

The SL631 is a family of Allwinner V3 action cameras sold under
various names, such as SJCAM SJ4000 Air or F60 Action Camera.

Devices in this family share a common board design but can be found
with different image sensors, including the IMX179 and the OV4689.

This adds support for a common dtsi for the SL631 family as well as
a specific dts for the IMX179 fashion, which will later be populated
with an IMX179 node when a driver is available.

Features that were tested on the device include:
- UART debug
- MMC
- USB peripheral (e.g. g_ether)
- Buttons
- SPI NOR flash

Note that the exact designer/vendor of these boards is unknown.

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20201206165131.1041983-6-contact@paulk.fr