esp8266/scripts: Don't try to create filesystem on 512KB devices or less.

There's no space for it.

esp8266/scripts/_boot.py

@@ -3,6 +3,7 @@ import builtins
 from flashbdev import bdev
 
 try:
+    if bdev:
         vfs = uos.VfsFat(bdev, "")
 except OSError:
     import inisetup

esp8266/scripts/flashbdev.py

@@ -26,4 +26,7 @@ class FlashBdev:
         if op == 5:  # BP_IOCTL_SEC_SIZE
             return self.SEC_SIZE
 
-bdev = FlashBdev()
+if esp.flash_size() < 1024*1024:
+    bdev = None
+else:
+    bdev = FlashBdev()