radv: export implicit primitive ID in NIR for legacy VS or TES

It's implicit for VS or TES, while it's required for GS or MS.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Timur Kristóf <timur.kristof@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16404>

src/amd/llvm/ac_nir_to_llvm.c

@@ -3684,6 +3684,8 @@ static void visit_intrinsic(struct ac_nir_context *ctx, nir_intrinsic_instr *ins
       } else if (ctx->stage == MESA_SHADER_TESS_EVAL) {
          result = ctx->tes_patch_id_replaced ? ctx->tes_patch_id_replaced
                                              : ac_get_arg(&ctx->ac, ctx->args->tes_patch_id);
+      } else if (ctx->stage == MESA_SHADER_VERTEX) {
+         result = ac_get_arg(&ctx->ac, ctx->args->vs_prim_id);
       } else
          fprintf(stderr, "Unknown primitive id intrinsic: %d", ctx->stage);
       break;