arch-x86: Use a namespace for integer registers.

Also reformat the integer register index constants to fit with the style
guide, ie remove the INTREG_ prefix (replaced by the namespace) and
captialize only the first letter.

Change-Id: I682a337944f64a1b96b971a1beb895289b9d299e
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/49752
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
20 files changed