py/mpconfig: Change the default enable level for the vfs module.

For boards with MICROPY_CONFIG_ROM_LEVEL_AT_LEAST_CORE_FEATURES and up.
This gets samd21 boards working (which need the vfs module in _boot.py),
B_L072Z_LRWAN1, and nrf boards with smaller MCUs that use CORE or BASIC
feature levels.

Signed-off-by: robert-hh <robert@hammelrath.com>

py/mpconfig.h

@@ -1746,7 +1746,7 @@ typedef double mp_float_t;
 
 // Whether to provide the "vfs" module
 #ifndef MICROPY_PY_VFS
-#define MICROPY_PY_VFS (MICROPY_CONFIG_ROM_LEVEL_AT_LEAST_EXTRA_FEATURES && MICROPY_VFS)
+#define MICROPY_PY_VFS (MICROPY_CONFIG_ROM_LEVEL_AT_LEAST_CORE_FEATURES && MICROPY_VFS)
 #endif
 
 #ifndef MICROPY_PY_WEBSOCKET