mimxrt: Add the Timer class to the machine module.

It supports three hardware timer channels based on the PIT timers of the
MIMXRT MCU.  The timer id's are 0, 1 and 2.  On soft reboot all active
timers will be stopped via finalisers.

ports/mimxrt/modmachine.c

@@ -29,6 +29,7 @@
 #include "extmod/machine_mem.h"
 #include "led.h"
 #include "pin.h"
+#include "modmachine.h"
 
 #include CPU_HEADER_H
 
@@ -54,6 +55,7 @@ STATIC const mp_rom_map_elem_t machine_module_globals_table[] = {
     { MP_ROM_QSTR(MP_QSTR_LED),                 MP_ROM_PTR(&machine_led_type) },
     #endif
     { MP_ROM_QSTR(MP_QSTR_Pin),                 MP_ROM_PTR(&machine_pin_type) },
+    { MP_ROM_QSTR(MP_QSTR_Timer),               MP_ROM_PTR(&machine_timer_type) },
 };
 STATIC MP_DEFINE_CONST_DICT(machine_module_globals, machine_module_globals_table);