dev,cpu: Make two very generic enums ScopedEnums.

dev,cpu: Make two very generic enums ScopedEnums.

Two python Enum parameter types had some very generic elements which
both include one named "none". When headers for both are included that
creates a conflict which breaks the build. Enums which such extremely
generic names need to be scoped so that they don't invite these sorts
of collisions.

This change converts them from Enum to ScopedEnum in python, and also
makes a few small changes to where they're used in c++ to match.

Issue-on: https://gem5.atlassian.net/browse/GEM5-447

Change-Id: Ibda6e6cfcd700a618f8c68d174f33ec1e178b9ac
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/27950
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>