mem: Move the Rank construction logic to the Rank constructor

mem: Move the Rank construction logic to the Rank constructor

This change was made so Rank objects have their name assigned
when they are instantiated. Therefore, they can initialize their
member objects with their name and it is less likely to change during
runtime.

(NOTE: I would recommend hiding the fields which would cause the name to
change behind getters. Since modification of `Rank.rank` during runtime
will cause the `name()` to change.)

Change-Id: Id51c3553b40e489792c57950e18b8ce927e43173
Signed-off-by: Sean Wilson <spwilson2@wisc.edu>
Reviewed-on: https://gem5-review.googlesource.com/3742
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>