tgsi: add Stream{X,Y,Z,W} fields to tgsi_declaration_semantic

tgsi: add Stream{X,Y,Z,W} fields to tgsi_declaration_semantic

This is for geometry shader outputs. Without it, drivers have no way of
knowing which stream each output is intended for, and have to
conservatively write all outputs to all streams.

Separate stream numbers for each component are required due to output
packing.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>