dt-bindings: memory-controller: Drop unneeded quotes

Cleanup bindings dropping unneeded quotes. Once all these are fixed,
checking for this can be enabled in yamllint.

Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230331182119.1899919-1-robh@kernel.org


Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>