python: Fix up arrow in interactive shell

Simply by importing the readline module, the up arrow will work in
gem5's interactive shell now.

Change-Id: I41d87adc34253abf5a00ac484da377f9f065a27a
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/62671
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>

src/python/m5/main.py

@@ -311,6 +311,8 @@ def interact(scope):
     else:
         # Use the Python shell in the standard library if IPython
         # isn't available.
+        import readline  # if this is imported, then the up arrow works
+
         code.InteractiveConsole(scope).interact(banner)