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

Convert the Exynos Mixer bindings to DT schema format.

The conversion includes also updates to the bindings, matching the
current DTS and Linux driver:
1. Add clocks required on Exynos4210 and Exynos4212 types of Mixer.
2. Add second memory range on Exynos4210 and Exynos4212.
3. Add interconnects, 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/20220208171823.226211-8-krzysztof.kozlowski@canonical.com