py: Make terse_arg_mismatch a global function and use it elsewhere.

Reduces code size when MICROPY_ERROR_REPORTING_TERSE is selected.
diff --git a/py/bc.c b/py/bc.c
index 47f8d9f..bbc9a20 100644
--- a/py/bc.c
+++ b/py/bc.c
@@ -62,9 +62,8 @@
 
 STATIC NORETURN void fun_pos_args_mismatch(mp_obj_fun_bc_t *f, mp_uint_t expected, mp_uint_t given) {
 #if MICROPY_ERROR_REPORTING == MICROPY_ERROR_REPORTING_TERSE
-    // Generic message, to be reused for other argument issues
-    nlr_raise(mp_obj_new_exception_msg(&mp_type_TypeError,
-        "argument num/types mismatch"));
+    // generic message, used also for other argument issues
+    mp_arg_error_terse_mismatch();
 #elif MICROPY_ERROR_REPORTING == MICROPY_ERROR_REPORTING_NORMAL
     nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_TypeError,
         "function takes %d positional arguments but %d were given", expected, given));