Tried this, and then am335x-boneblack.dtb threw errors...but I did get it working.
In the unlikely event that someone else wants to get this display working under Yocto (krogoth)...my first advice is don't. You're probably better off moving to a more recent Yocto and using Robert's file. But I'm under pressure to get this working, and my past experience is that changing to a new Yocto/kernel version would be another week's work IF there aren't any show stoppers. What I did was 1) translate the dts file into a format recognized by krogoth...I think the key issue was that it didn't like fragments...and 2) since touchscreen-swapped-x-y apparently wasn't supported, I had to swap the x and y sizes in the dts file, and hack the driver source to do the swapping. Oh, and the driver apparently had to be compiled into the kernel source, not loaded as a module.
I don't think it makes sense to share my (already obsolete) dts file or driver hack, but if someone wants it, I'll be happy to post.
John