zephyr/modmachine: Add machine.idle().

Signed-off-by: Damien George <damien@micropython.org>

ports/zephyr/modmachine.c

@@ -53,12 +53,19 @@ STATIC mp_obj_t machine_reset_cause(void) {
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_0(machine_reset_cause_obj, machine_reset_cause);
 
+STATIC mp_obj_t machine_idle(void) {
+    k_yield();
+    return mp_const_none;
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_0(machine_idle_obj, machine_idle);
+
 STATIC const mp_rom_map_elem_t machine_module_globals_table[] = {
     { MP_ROM_QSTR(MP_QSTR___name__), MP_ROM_QSTR(MP_QSTR_umachine) },
     #ifdef CONFIG_REBOOT
     { MP_ROM_QSTR(MP_QSTR_reset), MP_ROM_PTR(&machine_reset_obj) },
     #endif
     { MP_ROM_QSTR(MP_QSTR_reset_cause), MP_ROM_PTR(&machine_reset_cause_obj) },
+    { MP_ROM_QSTR(MP_QSTR_idle), MP_ROM_PTR(&machine_idle_obj) },
 
     #if MICROPY_PY_MACHINE_I2C
     { MP_ROM_QSTR(MP_QSTR_I2C), MP_ROM_PTR(&machine_hard_i2c_type) },