drm/radeon/r6xx/r7xx: CS parser fixes

- Drop some more safe regs taht userspace shouldn't hit
- Constant base regs need relocs.  This allows us to use
constant buffers rather than the constant register file.
Also we don't want userspace to be able to set arbitrary
mc base values for the const caches.
- Track SQ_CONFIG so we know whether userspace is using
the cfile or constant buffers.

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>