intel/compiler: MTL DF fixes

When I wrote these months ago, I had a simple GL test that would fail without these patches. For some reason that test doesn't fail anymore without these patches, and I can't even find a piglit that fails without these (edit: I found deqp tests that fail without these, see the comments). It seems other compiler changes may have affected how the instructions are handled. I'll keep looking for some test that fails without these, but in the meantime let's have the patches for review.

@currojerez: there's a patch from you here, it's still marked as WIP from you @jljusten: cc