mem: Use the new unbound port reporting mechanism in the mem ports.

mem: Use the new unbound port reporting mechanism in the mem ports.

There was an add-hoc check added to getAddrRanges, but the other methods
would just segfault if they tried to talk to their peers. This change
wraps all the calls in try blocks and catches the exception which the
peer will throw if it's the default and the port is not actually
connected to anything.

Change-Id: Ie46be0230f33f74305c599b251ca319a65ba008d
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/30296
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>