dt-bindings: media: samsung,exynos5250-gsc: convert to dtschema

Convert the Samsung Exynos SoC G-Scaler bindings to DT schema.

Changes done during conversion:
1. A typical (already used) properties like clocks, iommus and
   power-domains.
2. Require clocks, because they are essential for the block to operate.
3. Describe the differences in clocks between the Exynos5250/5420 and
   the Exynos5433 G-Scalers.  This includes the fifth Exynos5433 clock
   "gsd" (GSCL Smart Deck) which was added to the DTS, but not to the
   bindings and Linux driver.  Similarly to Exynos5433 DECON change [1],
   the clock should be used.

[1] https://lore.kernel.org/all/6270db2d-667d-8d6f-9289-be92da486c25@samsung.com/



Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220830180927.16686-1-krzysztof.kozlowski@linaro.org