scripts: Simplified dbgtag.py, tweaked -x/--hex decoding

This drops the option to read tags from a disk file. I don't think I've
ever used this, and it requires quite a bit of circuitry to implement.

Also dropped -s/--string, because most tags can't be represented as
strings?

And tweaked -x/--hex flags to correctly parse spaces in arguments, so
now these are equivalent:

- ./scripts/dbgtag.py -x 00 03 00 08
- ./scripts/dbgtag.py -x "00 03 00 08"

scripts/dbgflags.py

@@ -303,7 +303,7 @@ if __name__ == "__main__":
     import argparse
     import sys
     parser = argparse.ArgumentParser(
-            description="Decode littlefs error codes.",
+            description="Decode littlefs flags.",
             allow_abbrev=False)
     class AppendFlags(argparse.Action):
         def __call__(self, parser, namespace, value, option):