Hi @vivek338
The <board>_falcon_defconfig file is used to overwrite some configurations from the main configuration file .config. When enabling SPL_FS_FAT, the CONFIG_SPL_FS_LOAD_PAYLOAD_NAME has the default value: u-boot.itb, so no need to overwrite this. You can take a look over the .config file and check that the CONFIG_SPL_FS_LOAD_PAYLOAD_NAME has the correct value.
Regarding the selection of the folder in imx-mkimage, for i.MX 8M Mini, i.MX 8M Nano or i.MX 8M Plus, you should use the i.MX8M folder.
According to your log, you are not in Falcon Mode, since you reached the U-Boot console. In Falcon Mode the Kernel is started right after SPL. How did you enter in U-Boot, by pressing the 'C' key? If you want to boot in Falcon Mode, you don't need to press any key.
Please make sure you have u-boot.itb, Image.itb and imx8mm-evk-falcon.dtb on the boot partition of the SD card.
Did you use the prebuild image imx-image-full-imx8mmevk.wic? If yes, the imx8mm-evk.dtb file should be in the boot partition of the SD card.
Can you tell me the steps you've done so far? Just to make sure you didn't skip any of them. There are quite a few steps and it's very easy to miss one.
Thank you,
Elena