kern: Replace an explicitly instantiated port proxy with one from the tc.

kern: Replace an explicitly instantiated port proxy with one from the tc.

That avoids having to know what type of proxy to create.

Change-Id: I311e770ab720061b52f29df0dcc2273e028aa34a
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/18578
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Brandon Potter <Brandon.Potter@amd.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>