intel/compiler: More EU and compiler IR validation
These come from some other work that I was doing, but I think it's going to be a bit longer before that's ready. In the meantime, we can add these extra validations. The 3-source and CSEL
validations would have caught the problems when I added support for CSEL
instructions some years ago. Going forward, I believe that any MR that adds support for a new instruction should also add validation.