python: Add Python 3 workarounds for long

python: Add Python 3 workarounds for long

Python 3 doesn't have a separate long type. Make long an alias for int
where needed to maintain compatibility.

Change-Id: I4c0861302bc3a2fa5226b3041803ef975d29b2fd
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/15988
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>