ARM: dts: sunxi: add support for Anbernic RG-Nano

ARM: dts: sunxi: add support for Anbernic RG-Nano

The Anbernic RG-Nano is a small portable game device based on the
Allwinner V3s SoC. It has GPIO buttons on the face and side for
input, a single mono speaker, a 240x240 SPI controlled display, a USB-C
OTG port, an SD card slot for booting, and 64MB of RAM included in the
SoC. There does not appear to be a crystal feeding the internal RTC so
it does not keep proper time (for me it ran 8 hours slow in a 24 hour
period). External RTC works just fine.

Working/Tested:
- SDMMC
- UART (for debugging)
- Buttons
- Charging/battery/PMIC
- Speaker
- RTC (external RTC)
- USB
- Display

Signed-off-by: Chris Morgan <macromorgan@hotmail.com>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Reviewed-by: Samuel Holland <samuel@sholland.org>
Link: https://lore.kernel.org/r/20230929144441.3409-5-macroalpha82@gmail.com
Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>