intel: Add field intel_mipmap_slice::has_hiz

intel: Add field intel_mipmap_slice::has_hiz

On Haswell, HiZ will selectively be enabled on individual miptree slices
to workaround a hardware bug. The new field 'has_hiz' indicates if HiZ is
enabled for a given slice.

Also add two new accessor functions for this field.
  intel_miptree_slice_has_hiz
  intel_renderbuffer_has_hiz

The new field and accessor functions are not yet used. Also, this patch
introduces no behavioral change because, in this patch,
intel_miptree_alloc_hiz() sets has_hiz for all slices.

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