nrf/main: Execute boot.py/main.py frozen modules without a file system.

When the file system is not enabled, the boot.py and main.py modules will
still be executed, if they are frozen.

ports/nrf/main.c

@@ -230,7 +230,7 @@ pin_init0();
 
 led_state(1, 0);
 
-#if MICROPY_VFS || MICROPY_MBFS
+#if MICROPY_VFS || MICROPY_MBFS || MICROPY_MODULE_FROZEN
     // run boot.py and main.py if they exist.
     pyexec_file_if_exists("boot.py");
     pyexec_file_if_exists("main.py");