esp8266: Convert to use new MP_Exxx errno symbols.

These symbols are still defined in terms of the system Exxx symbols, and
can be switched to internal numeric definitions at a later stage.

Note that extmod/modlwip still uses many system Exxx symbols.
diff --git a/esp8266/moduos.c b/esp8266/moduos.c
index d75062e..bc2838d 100644
--- a/esp8266/moduos.c
+++ b/esp8266/moduos.c
@@ -25,7 +25,6 @@
  */
 
 #include <string.h>
-#include <errno.h>
 
 #include "py/mpconfig.h"
 #include "py/nlr.h"
@@ -33,6 +32,7 @@
 #include "py/objtuple.h"
 #include "py/objstr.h"
 #include "py/runtime.h"
+#include "py/mperrno.h"
 #include "extmod/misc.h"
 #include "genhdr/mpversion.h"
 #include "esp_mphal.h"
@@ -74,7 +74,7 @@
 #if MICROPY_VFS_FAT
 mp_obj_t vfs_proxy_call(qstr method_name, mp_uint_t n_args, const mp_obj_t *args) {
     if (MP_STATE_PORT(fs_user_mount)[0] == NULL) {
-        nlr_raise(mp_obj_new_exception_arg1(&mp_type_OSError, MP_OBJ_NEW_SMALL_INT(ENODEV)));
+        nlr_raise(mp_obj_new_exception_arg1(&mp_type_OSError, MP_OBJ_NEW_SMALL_INT(MP_ENODEV)));
     }
 
     mp_obj_t meth[n_args + 2];