type_size sanity
In the process of fixing up nir-to-tgsi, I needed the glsl type size functions from gallium drivers, so they need to be in a shared location. That led me to finding that nir-to-tgsi isn't the only one needing those functions and we just had code duplication.
I suspect i965's remaining type size functions might be possible to be simplified as well, but they were less obvious.