Parametrize the SWF registers. This also fixes the register offsets,
which were mostly garbage in the old defines.

Also save/restore only as many SWF registers that each platform has.
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NJesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>