Where do you do the modification of the dtsi file? Is it under the boot2qt build? If so it could be that you have to force the recompilation of the kernel with:
bitbake -fc compile virtual/kernel
bitbake <image name>
Yocto doesn’t recognize modifications in the build directories.
However, as an alternative you can also checkout the following repository:
Then you can do your modification on the devicetree and afterwards recompile it as described here:
To compile the devictree file you can do something like this:
The compiled dtb will be under arch/arm/boot/dts/imx7d-colibri-emmc-eval-v3.dtb. You can then copy this devictree binary to the target.
I hope this helps.