Faith Ekstrand authored May 29, 2020 and Erik Faye-Lund committed Aug 05, 2020

There are a few cases, atomic counters being one example, where the type
used by vtn_ssa_value is not the same as the type we want NIR to use in
derefs and variables.  To solve this, we add a helper which converts
between the types for us.  In the next commit, we'll be adding another
major user of this: images and samplers.

Part-of: <mesa/mesa!5278>