GEN6_GT_THREAD_STATUS_REG doesn't seem to exist on VLV. Reads just give
0x0 no matter what the state of the render and media wells.

There was also some hint in the Gunit HAS that thread status not being
needed on VLV, and hence dropped when bringing stuff over from the IVB
design. Not really a definite comment about the specific register itself
though.

Also the w/a itself is no longer listed for VLV in the database. It was
there some time ago in the past, but I guess someone figured out the
mistake and dropped it.

So let's just drop it from the code as well.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Deepak S<deepak.s@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>