ARM: dts: imx8mm-verdin: dm-spl for pinctrl_usdhc1 node

Let pinctrl configuration for eMMC node (usdhc1) also be
accessible in SPL.

Signed-off-by: Igor Opaniuk <igor.opaniuk@toradex.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Oleksandr Suvorov <oleksandr.suvorov@toradex.com>