drm/i915: Change VLV WIZ hashing mode to 16x4

We set the WIZ hashing mode to 16x4 for all the other gen6+
platfotrms, so let's follow suit on VLV.

My VLV is AWOL currently so I didn't test this, but since the results
for all the other platforms agree that 16x4 is the fastest we might
assume the same holds for VLV.

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