arch-x86: Convert the int register constants from RegIndex to RegId.

This will let them be used in APIs which expect either, and will help
transition between the two.

Change-Id: I73fc9e55418ad3ab9e08406f0928aa4b1ef30a49
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/49754
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
3 files changed