py: Change first arg of type.make_new from mp_obj_t to mp_obj_type_t*.

The first argument to the type.make_new method is naturally a uPy type,
and all uses of this argument cast it directly to a pointer to a type
structure.  So it makes sense to just have it a pointer to a type from
the very beginning (and a const pointer at that).  This patch makes
such a change, and removes all unnecessary casting to/from mp_obj_t.
diff --git a/py/objobject.c b/py/objobject.c
index 5cd3773..bba6f05 100644
--- a/py/objobject.c
+++ b/py/objobject.c
@@ -33,11 +33,11 @@
     mp_obj_base_t base;
 } mp_obj_object_t;
 
-STATIC mp_obj_t object_make_new(mp_obj_t type_in, size_t n_args, size_t n_kw, const mp_obj_t *args) {
+STATIC mp_obj_t object_make_new(const mp_obj_type_t *type, size_t n_args, size_t n_kw, const mp_obj_t *args) {
     (void)args;
     mp_arg_check_num(n_args, n_kw, 0, 0, false);
     mp_obj_object_t *o = m_new_obj(mp_obj_object_t);
-    o->base.type = MP_OBJ_TO_PTR(type_in);
+    o->base.type = type;
     return MP_OBJ_FROM_PTR(o);
 }
 
@@ -54,7 +54,7 @@
                     "__new__ arg must be a user-type"));
     }
     mp_obj_t o = MP_OBJ_SENTINEL;
-    mp_obj_t res = mp_obj_instance_make_new(cls, 1, 0, &o);
+    mp_obj_t res = mp_obj_instance_make_new(MP_OBJ_TO_PTR(cls), 1, 0, &o);
     return res;
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_1(object___new___fun_obj, object___new__);