arm64: dts: meson-g12b-odroid-n2: add missing amlogic, s922x compatible

This fixes the following DT schemas check errors:
meson-g12b-odroid-n2.dt.yaml: /: compatible: ['hardkernel,odroid-n2', 'amlogic,g12b'] is not valid under any of the given schemas

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>