dt-bindings: display: bridge: parade,ps8622: convert to dtschema

Convert the Parade PS8622/PS8625 DisplayPort to LVDS Converter bindings
to DT schema. Changes during conversion: add missing vdd12-supply, used
by Linux driver.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230221170955.62448-1-krzysztof.kozlowski@linaro.org
Signed-off-by: Rob Herring <robh@kernel.org>