arch-x86, kvm: clean up x86 long regresion kvm code

arch-x86, kvm: clean up x86 long regresion kvm code

This commit cleans up the code for x86 kvm long regressions.
Somehow the old version went is as the last patchset.
This is the intended code, which should match the last comments.

Change-Id: I9af02a51ce8ed5098887fb0a6b9240db95227bc3
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/37120
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>