python: Apply Black formatter to Python files

The command executed was `black src configs tests util`.

Change-Id: I8dfaa6ab04658fea37618127d6ac19270028d771
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/47024
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/sim/SubSystem.py

@@ -45,9 +45,9 @@ from m5.params import *
 # any naming conflicts.
 #
 class SubSystem(SimObject):
-    type = 'SubSystem'
+    type = "SubSystem"
     cxx_header = "sim/sub_system.hh"
-    cxx_class = 'gem5::SubSystem'
+    cxx_class = "gem5::SubSystem"
     abstract = False
 
     # Thermal domain associated to this object, inheriting the parent's