Rework CL work ID offset system values

This series undoes the nir/vtn bits of !106 (merged) and replaces them with mesa/mesa!5891 (merged). More or less the same, but with slightly different intrinsic and option names. Again, not sure what the best way is to synchronize our tree with upstream short of a full rebase, but I'm hoping this eases the burden of the next rebase.

Upstream bits have landed now, so I've applied the final commits here.