mmc: sdhci-esdhc-imx: add CMDQ support

Add CMDQ support for imx8qm/imx8qxp.

Signed-off-by: Haibo Chen <haibo.chen@nxp.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
[Ulf: Rebased on top of latest changes]
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>