arm64: dts: mediatek: Add missing chassis-type to MT8192 Chromebooks

None of the MT8192 Chromebooks had their chassis-type specified: add
the right definition for each.

Reviewed-by: David Heidelberg <david@ixit.cz>
Link: https://lore.kernel.org/r/20240313141538.1438167-3-angelogioacchino.delregno@collabora.com


Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>