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>