py/parse: Make mp_parse_node_new_leaf an inline function.

It is split into 2 functions, one to make small ints and the other to make
a non-small-int leaf node.  This reduces code size by 32 bytes on
bare-arm, 64 bytes on unix (x64-64) and 144 bytes on stmhal.
diff --git a/py/parse.h b/py/parse.h
index 54bbd26..769f5a8 100644
--- a/py/parse.h
+++ b/py/parse.h
@@ -76,7 +76,12 @@
 #define MP_PARSE_NODE_STRUCT_KIND(pns) ((pns)->kind_num_nodes & 0xff)
 #define MP_PARSE_NODE_STRUCT_NUM_NODES(pns) ((pns)->kind_num_nodes >> 8)
 
-mp_parse_node_t mp_parse_node_new_leaf(size_t kind, mp_int_t arg);
+static inline mp_parse_node_t mp_parse_node_new_small_int(mp_int_t val) {
+    return (mp_parse_node_t)(MP_PARSE_NODE_SMALL_INT | ((mp_uint_t)val << 1));
+}
+static inline mp_parse_node_t mp_parse_node_new_leaf(size_t kind, mp_int_t arg) {
+    return (mp_parse_node_t)(kind | ((mp_uint_t)arg << 4));
+}
 bool mp_parse_node_is_const_false(mp_parse_node_t pn);
 bool mp_parse_node_is_const_true(mp_parse_node_t pn);
 bool mp_parse_node_get_int_maybe(mp_parse_node_t pn, mp_obj_t *o);