dt-bindings: mmc: sdhci-am654: cleanup style

Cleanup coding style without functional changes:
1. Drop unnecessary quotes from $ref.
2. Use simple enum for compatible enumeration and sort entries.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20221204094717.74016-2-krzysztof.kozlowski@linaro.org


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>