mem-ruby: change MessageBuffer randomization param

mem-ruby: change MessageBuffer randomization param

There are cases in which we need to prevent randomization for a
specific buffer when enabled at the RubySystem level (e.g. a internal
trigger queue that requires zero latency enqueue, while other buffers
can be randomized).

This changes the randomization parameter to support enabling and
disabling randomization regardless of the RubySystem setting.

Change-Id: If7520153cc5864897fa42e8911a6f8acbcf01db5
Signed-off-by: Tiago Mück <tiago.muck@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/31419
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>