gallivm/nir: add support for multiple vertex streams

This adds support to the nir shader build for multiple vertex streams
we store separate stats for each stream, then write them out in the epilogue.

Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3530>
2 files changed