Hello @Deepak1,
I have not tried out loading the firmware from the DDR RAM myself, but I can give you some pointers on how to do that.
From the file boards/mekmimx8qx/demo_apps/hello_world/armgcc/MIMX8QX6xxxxx_cm4_ddr_ram.ld in the SDK directory, you will find the memory addresses for the DDR RAM that you will need to add into the reserved-memory section in the device-tree overlay file. So you will have to add a memory for section m_data and m_data2 into the reserved-memory (either as two separate nodes or one node with the added lengths).
m_data (RW) : ORIGIN = 0x88200000, LENGTH = 0x00200000
m_data2 (RW) : ORIGIN = 0x88400000, LENGTH = 0x07C00000
After that, you can compile and apply the device tree overlay. Then, build the firmware with the script build_ddr_debug.sh or build_ddr_release.sh in the armgcc directory.
You will have to change the load address for the firmware to this new starting address of the DDR RAM and also change the size of the memory to the size of the firmware binary. Here is an example for how to do this: Run simply Hello world" M4 application in DDR - #5 by bruno.tx
Let me know if this helps.