arm64: dts: amlogic: Add Ugoos AM3

arm64: dts: amlogic: Add Ugoos AM3

The Ugoos AM3 is a small set-top box based on the Amlogic S912 SoC,
with a board design that is very close to the Q20x development boards.
The MMC max-frequency properties are copied from the downstream device
tree.

  https://ugoos.com/ugoos-am3-16g

The following functionality has been tested and is known to work:
 - debug serial port
 - "update" button inside the case
 - USB host mode, on all three ports
 - HDMI video/audio output
 - eMMC, MicroSD, and SDIO WLAN
 - S/PDIF audio output
 - Ethernet
 - Infrared remote control input

The following functionality doesn't seem to work:
 - USB role switching and device mode on the "OTG" port
 - case LED

Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: J. Neuschäfer <j.ne@posteo.net>
Link: https://lore.kernel.org/r/20250613-ugoos-am3-v3-2-f8a43e6bbfdb@posteo.net
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>