python: Switch to the new getPort mechanism to connect ports.

python: Switch to the new getPort mechanism to connect ports.

This retrieves ports using the getPort method, and connects them using
the bind method on the ports themselves. Any smarts as far as what type
of peers are allowed to connect or how they connect is left up to the
individual bind methods.

Change-Id: Ic640d1fce8af1bed411116e5830edc4a8a0f9d66
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/17039
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>