cpu: Switch away from some fringe Request constructors.

cpu: Switch away from some fringe Request constructors.

These are only used in these two files, one each, and pass one dummy
argument with a default value and one extra argument with an actual
value compared to the more common constructors.

Instead, switch to constructors without those two arguments and set the
one extra value explicitly after construction.

The constructor will likely be inlined, and merged with this additional
assignment.

Change-Id: I75ca539d5ca95b57b4f4322ffa050af2031544dd
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/26229
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Gabe Black <gabeblack@google.com>