python: Replace deprecated repr syntax

Change-Id: I5f9538cf2ca5ee17c51e7c5388d3aef363fcfa54
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/15989
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>

src/python/m5/util/sorteddict.py

@@ -214,7 +214,7 @@ if __name__ == '__main__':
     d['y'] = 26
     display(d)
 
-    print(`d`)
+    print(repr(d))
 
     print(d.copy())