After the previous patch the GEN8 RPS handler became very similar to the
GEN6 version, so unify the two functions.

No functional change.
Signed-off-by: NImre Deak <imre.deak@intel.com>
Reviewed-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
[danvet: Move one misplaced hunk from a later patch to fix a bisect
issue as reported by Wu Fengguang's 0-day builder and fix suggested by
Imre.]
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>