Currently, I have imx6 evaluation board. I tried booting from both TFTP and sd-card.
Now, I need to take kernel(uimage and dtb files) from sd-card but with NFS filesystem.
what are the changes I have to do in boot.scr file.
I suggest you follow the below document. There you could find how to perform the action that you are willing to have. I have followed before the document and I can confirm that the solution works.