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>

.pre-commit-config.yaml

@@ -44,7 +44,7 @@ exclude: |
     build/.*|
     src/systemc/ext/.*|
     src/systemc/tests/.*/.*|
-    src/python/m5/ext/.*|
+    src/python/m5/ext/pyfdt/.*|
     tests/.*/ref/.*
   )$
 

src/python/m5/ext/pystats/group.py

@@ -40,6 +40,7 @@ from .serializable_stat import SerializableStat
 from .statistic import Scalar, Statistic
 from .timeconversion import TimeConversion
 
+
 class Group(SerializableStat):
     """
     Used to create the heirarchical stats structure. A Group object contains a

src/python/m5/ext/pystats/serializable_stat.py

@@ -30,6 +30,7 @@ from typing import Dict, List, Union, Any, IO
 
 from .storagetype import StorageType
 
+
 class SerializableStat:
     """
     Classes which inherit from SerializableStat can be serialized as JSON

src/python/m5/ext/pystats/simstat.py

@@ -32,6 +32,7 @@ from .group import Group
 from .statistic import Statistic
 from .timeconversion import TimeConversion
 
+
 class SimStat(SerializableStat):
     """
     Contains all the statistics for a given simulation.