dt-bindings: display: mediatek: simplify compatibles syntax

Lists (items) with one item should be just enum because it is shorter,
simpler and does not confuse, if one wants to add new entry with a
fallback.  Convert all of them to enums.  OTOH, leave unused "oneOf"
entries in anticipation of further growth of the entire binding.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Link: https://lore.kernel.org/r/20230414083311.12197-1-krzysztof.kozlowski@linaro.org


Signed-off-by: Rob Herring <robh@kernel.org>