v3d: implement geometry shader instancing

v2:
 - Remove unused field uses_iid from v3d_gs_prog_data (Alejandro)

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>

src/broadcom/compiler/nir_to_vir.c

@@ -2327,6 +2327,10 @@ ntq_emit_intrinsic(struct v3d_compile *c, nir_intrinsic_instr *instr)
                 break;
         }
 
+        case nir_intrinsic_load_invocation_id:
+                ntq_store_dest(c, &instr->dest, 0, vir_IID(c));
+                break;
+
         default:
                 fprintf(stderr, "Unknown intrinsic: ");
                 nir_print_instr(&instr->instr, stderr);