i965/blorp: Enable blorp blits on Gen7.

i965/blorp: Enable blorp blits on Gen7.

Gen7 support for blorp (blits using the render bath) now works for
non-MSAA purposes.  This patch enables it.

Since blorp operations re-use the logic for HiZ ops, this required
adding a case to the switch statement in gen7_blorp_emit_wm_config(),
to allow for the case where no HiZ op is being performed.

Reviewed-by: Chad Versace <chad.versace@linux.intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>