stmhal: Execute boot.py and main.py when formatting the file system.

When you use the USER button to perform a filesystem reset
at boot time then it wipes out the filesystem and creates
a new boot.py and main.py.  With this patch these files are
executed after formatting, ensuring that pyb and machine modules
get imported.

stmhal/main.c

@@ -529,7 +529,7 @@ soft_reset:
 
     // run boot.py, if it exists
     // TODO perhaps have pyb.reboot([bootpy]) function to soft-reboot and execute custom boot.py
-    if (reset_mode == 1) {
+    if (reset_mode == 1 || reset_mode == 3) {
         const char *boot_py = "boot.py";
         FRESULT res = f_stat(boot_py, NULL);
         if (res == FR_OK) {
@@ -585,7 +585,7 @@ soft_reset:
     // At this point everything is fully configured and initialised.
 
     // Run the main script from the current directory.
-    if (reset_mode == 1 && pyexec_mode_kind == PYEXEC_MODE_FRIENDLY_REPL) {
+    if ((reset_mode == 1 || reset_mode == 3) && pyexec_mode_kind == PYEXEC_MODE_FRIENDLY_REPL) {
         const char *main_py;
         if (MP_STATE_PORT(pyb_config_main) == MP_OBJ_NULL) {
             main_py = "main.py";