arch: arm: dts: imx8mm-cl-iot-gate.dts: add no-mmc-hs400 to mmc2

arch: arm: dts: imx8mm-cl-iot-gate.dts: add no-mmc-hs400 to mmc2

The eMMC device on imx8mm-cl-iot-gate seems not support hs400.
When booting 6.1.0 kernel we got the following error.

    mmc2: mmc_select_hs400es failed, error -110
    mmc2: error -110 whilst initialising MMC card

Add no-mmc-hs400 to mmc2 node solves the problem.

Signed-off-by: Ying-Chun Liu (PaulLiu) <paul.liu@linaro.org>
Cc: Tom Rini <trini@konsulko.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: NXP i.MX U-Boot Team <uboot-imx@nxp.com>