mem: Add a Request::Flags parameter to the translating port proxies.

mem: Add a Request::Flags parameter to the translating port proxies.

These flags will be given to the Request object which is used to do the
translation.

Change-Id: I21755f5f9369311e2f2d5be73ebd4f5865f73265
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/26623
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Matthew Poremba <matthew.poremba@amd.com>
Maintainer: Gabe Black <gabeblack@google.com>