dt-bindings: mmc: convert orion-sdio to JSON schema

Convert the orion-sdio binding to JSON schema.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20220419024611.1327525-4-chris.packham@alliedtelesis.co.nz
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>