i965/gen7: Enable HiZ

i965/gen7: Enable HiZ

This patch modifies all batches needed for HiZ. The batch length for
3DSTATE_HIER_DEPTH_BUFFER is also corrected from 4 to 3.

Performance +6.7% on Citybench.
    num-frames: 400
    resolution: 1918x1031
    avg-hiz-off: 127.90 fps
    avg-hiz-on: 136.50 fps
    kernel: git://people.freedesktop.org/~anholt/linux.git branch=gen7-reset-sol sha=23360e4

Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Signed-off-by: Chad Versace <chad.versace@linux.intel.com>