drm/i915: Make vlv and chv forcewake put generic.

These two were using a fw dance logic where posting read was done
after both domain bit were set. When in other gens, the posting
read is done immediately after setting the forcewake bit for each
domain.

Now bring these in line with other gens.

Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Deepak S <deepak.s@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>