misc: Update black to process src/python/m5/ext/pystats

The exclusion in .pre-commit-config.yaml covered all files in
src/python/m5/ext. This excludes src/python/m5/exit/pystats, which we
want covered by black. This commit updates .pre-commit-config.yaml to
only exclude src/python/m5/ext/pyfdt.

This change also runs black on these files.

Change-Id: Iecff45ea2a27a37fc0d00b867d41300aad911c7a
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/63711
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
4 files changed