nir: add rasterization_stream sysval

for plumbing transformFeedbackRasterizationStreamSelect (in turn for exercising
more CTS and proving out my design).

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Mary Guillemard <mary.guillemard@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35802>

src/compiler/nir/nir_divergence_analysis.c

@@ -254,6 +254,7 @@ visit_intrinsic(nir_intrinsic_instr *instr, struct divergence_state *state)
    case nir_intrinsic_load_line_width:
    case nir_intrinsic_load_aa_line_width:
    case nir_intrinsic_load_xfb_address:
+   case nir_intrinsic_load_rasterization_stream:
    case nir_intrinsic_load_num_vertices:
    case nir_intrinsic_load_fb_layers_v3d:
    case nir_intrinsic_load_fep_w_v3d:

src/compiler/nir/nir_intrinsics.py

@@ -1012,6 +1012,9 @@ system_value("xfb_size", 1, bit_sizes=[32], indices=[BASE])
 # from the index buffer.
 system_value("xfb_index_buffer", 1, bit_sizes=[32,64])
 
+# Currently active rasterization stream [0..3]
+system_value("rasterization_stream", 1)
+
 system_value("frag_size", 2)
 system_value("frag_invocation_count", 1)
 # Whether smooth lines or polygon smoothing is enabled