python,scons: Break slicc's dependence on m5.util.

The only dependence remaining was a small utility function makeDir which
was only used by slicc. This change moves it to where it's used, and
cleans up the additions to sys.path a little.

Change-Id: I7415b53ea2e9c378b6dbf342b8b3a966f48e117c
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/49397
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Hoa Nguyen <hoanguyen@ucdavis.edu>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>

src/python/m5/util/__init__.py

@@ -155,15 +155,6 @@ def printList(items, indent=4):
             line += item
             print(line)
 
-def makeDir(path):
-    """Make a directory if it doesn't exist.  If the path does exist,
-    ensure that it is a directory"""
-    if os.path.exists(path):
-        if not os.path.isdir(path):
-            raise AttributeError("%s exists but is not directory" % path)
-    else:
-        os.mkdir(path)
-
 def isInteractive():
     """Check if the simulator is run interactively or in a batch environment"""