dt-bindings: mmc: Add supports-cqe property

Add supports-cqe optional property for MMC hosts.

This property is used to identify the specific host controller
supporting command queue.

Signed-off-by: Sowjanya Komatineni <skomatineni@nvidia.com>
Reviewed-by: Thierry Reding <treding@nvidia.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>