Where are the built blobs supposed to go? I tried it, it built the blobs, but I can't find them anywhere.
Nevermind, I found it on yocto's tmp/work dir. I was expecting them to be on the kernel source dir.
One last note: make dtbs will build all dtbs. You can build just the dtb you want using, make <dtbname>.dtb
Beware you need the .dtb in the end. Also that the base dir is arch/arm/boot/dts, so if you want a dtb inside a sub-dir you must include it in the name:
make freescale/dtbname.dtb