python: Add support for scoped enums

python: Add support for scoped enums

At the moment gem5 has support for enum params that either generate a
unscoped within the Enums namespace or a struct encapsulated enum. The
Enums namespace is getting quite big and some params have the same
names which results in collisions. This change adds support for the
scoped enums.

Change-Id: I930e1cc3b814081627b653939e75d6c43956a334
Signed-off-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/15395
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>