arch: Fix all override related warnings.

Clang has started(?) reporting override related warnings, something gcc
apparently did before, but was disabled in the SConstruct. Rather than
disable the warnings in for clang as well, this change fixes the
warnings. A future change will re-enable the warnings for gcc.

Change-Id: I3cc79e45749b2ae0f9bebb1acadc56a3d3a942da
Reviewed-on: https://gem5-review.googlesource.com/9343
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Gabe Black <gabeblack@google.com>

sparc: Pull flat static instruction classes out of the ISA.

These classes are just used as base classes for other instructions
and don't need to be part of the ISA definition. Pull them into
standard C++ files.

Change-Id: If3e0bd82b1e676f20459bc0293fbda49de66b554
Reviewed-on: https://gem5-review.googlesource.com/5422
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>