drm/i915/chv: Combine GEN8_ROW_CHICKEN w/a

WaDisablePartialInstShootdown:chv and
WaDisableThreadStallDopClockGating:chv are related to the same
register so combine them.

Signed-off-by: Arun Siluvery <arun.siluvery@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>