spirv2dxil: Support basic subgroups

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20777>

src/microsoft/spirv_to_dxil/dxil_spirv_nir.c

@@ -866,6 +866,9 @@ dxil_spirv_nir_passes(nir_shader *nir,
 
    NIR_PASS_V(nir, nir_lower_system_values);
 
+   NIR_PASS_V(nir, dxil_nir_lower_subgroup_id);
+   NIR_PASS_V(nir, dxil_nir_lower_num_subgroups);
+
    // Force sample-rate shading if we're asked to.
    if (conf->force_sample_rate_shading) {
       assert(nir->info.stage == MESA_SHADER_FRAGMENT);

src/microsoft/spirv_to_dxil/spirv_to_dxil.c

@@ -60,6 +60,7 @@ spirv_to_dxil(const uint32_t *words, size_t word_count,
       .caps = {
          .draw_parameters = true,
          .multiview = true,
+         .subgroup_basic = true,
       },
       .ubo_addr_format = nir_address_format_32bit_index_offset,
       .ssbo_addr_format = nir_address_format_32bit_index_offset,