pbkwarg: add option for default enum element
This way, a default argument can be an Enum element.
// Optional keyword argument with default integer value
#define PB_ARG_DEFAULT_INT(name, value) (name, MP_ARG_OBJ, {.u_obj = MP_OBJ_NEW_SMALL_INT(value)} )
+// Optional keyword argument with default enum value
+#define PB_ARG_DEFAULT_ENUM(name, enum_elem) (name, MP_ARG_OBJ, {.u_rom_obj = MP_OBJ_FROM_PTR(&enum_elem)} )
+
// Optional keyword argument with default false value
#define PB_ARG_DEFAULT_FALSE(name)(name, MP_ARG_OBJ, {.u_rom_obj = MP_ROM_PTR(&mp_const_false_obj)})
