The SDMA firmware does not load automatically. I can find the /lib/firmware/imx/sdma/sdma-imx7d.bin and the dts points to the exact location.
The udev script needs to be implemented to load the firmware seperately which is executed after the default timeout of 60 secs. Am I missing any config in kernel? I could not see the same issue with iMX8MM EVK eval kit with IMX image with 4.14.