Hello Srikanth,
Yes only ELF format is supported because it contains information about binary location you don't have obviously in the .bin format.
By the way, we support .bin firmware but in this case this is for firmware signed (so for authentication at start up) because this binary is associated with additional tables. But My understanding is not what you want to do (if you are interested, the wiki is describing this more complex use case...).
Also note, on V5 release there was a regression on the feature (M4 load from U-boot). It was solved with this patch:
https://github.com/STMicroelectronics/linux/commit/89fdf7bece3d1be0d37156897ed8e183d5fcf1e4
