arm64: dts: meson: add g12a x96 max board

Add the G12a (S905X2) based X96 Max board[1].

There is no branding for the manufacturer anywhere on the product, so it
took some digging[2] to find the manufacturer.  But since there's
nothing about the maker on the product I've left it out of the DT name
because 1) nobody will know that name and 2) keeps the DT filename
shorter.

[1] https://www.cnx-software.com/2018/09/25/x96-max-amlogic-s905x2-tv-box/
[2] https://fccid.io/2AI6D-X96MAX



Acked-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>