dt-bindings: display: samsung,exynos-fimd: convert to dtschema

Convert the S3C/S5P/Exynos FIMD bindings to DT schema format.

The conversion includes also updates to the bindings, matching the
current DTS and Linux driver: adding optional iommus and power-domains.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220208171823.226211-11-krzysztof.kozlowski@canonical.com