dt-bindings: display/msm: gpu: Simplify conditional schema logic

dt-bindings: display/msm: gpu: Simplify conditional schema logic

JSON Schema conditionals can become complex and error-prone when combined
with regex patterns. To improve readability and maintainability, replace
nested if-else blocks with a flattened structure using explicit enums.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Signed-off-by: Akhil P Oommen <akhilpo@oss.qualcomm.com>
Patchwork: https://patchwork.freedesktop.org/patch/696674/
Message-ID: <20251231-qcs615-spin-2-v6-2-da87debf6883@oss.qualcomm.com>
Signed-off-by: Rob Clark <robin.clark@oss.qualcomm.com>