stm32: Allow to build with threading with the GIL disabled.

ports/stm32/gccollect.c

@@ -27,7 +27,7 @@
 #include <stdio.h>
 #include <stdint.h>
 
-#include "py/obj.h"
+#include "py/mpstate.h"
 #include "py/gc.h"
 #include "py/mpthread.h"
 #include "lib/utils/gchelper.h"

ports/stm32/mpthreadport.c

@@ -26,6 +26,7 @@
 
 #include <stdio.h>
 
+#include "py/mpstate.h"
 #include "py/gc.h"
 #include "py/mpthread.h"
 #include "gccollect.h"