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>

util/slicc

@@ -31,7 +31,6 @@ if __name__ == "__main__":
 
     base = dirname(__file__)
     sys.path.insert(1, join(base, "../src/mem"))
-    sys.path.insert(1, join(base, "../src/python"))
     sys.path.insert(1, join(base, "../build_tools"))
     sys.path.insert(1, join(base, "../ext/ply"))