radeonsi: implement VERTEXID_NOBASE and BASEVERTEX system values

Only done for completeness. Not used by anything yet.

Tested by advertising PIPE_CAP_VERTEXID_NOBASE.

Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
diff --git a/src/gallium/drivers/radeonsi/si_shader.c b/src/gallium/drivers/radeonsi/si_shader.c
index e93708b..42febe2 100644
--- a/src/gallium/drivers/radeonsi/si_shader.c
+++ b/src/gallium/drivers/radeonsi/si_shader.c
@@ -598,6 +598,16 @@
 						  SI_PARAM_BASE_VERTEX), "");
 		break;
 
+	case TGSI_SEMANTIC_VERTEXID_NOBASE:
+		value = LLVMGetParam(radeon_bld->main_fn,
+				     si_shader_ctx->param_vertex_id);
+		break;
+
+	case TGSI_SEMANTIC_BASEVERTEX:
+		value = LLVMGetParam(radeon_bld->main_fn,
+				     SI_PARAM_BASE_VERTEX);
+		break;
+
 	case TGSI_SEMANTIC_SAMPLEID:
 		value = get_sample_id(radeon_bld);
 		break;