anv: Add support for the PMA fix on Broadwell

anv: Add support for the PMA fix on Broadwell

This helps Dota 2 on Broadwell by 8-9%.  I also hacked up the driver and
used the Sascha "shadowmapping" demo to get some results.  Setting
uses_kill to true dropped the framerate on the demo by 25-30%.  Enabling
the PMA fix brought it back up to around 90% of the original framerate.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Nanley Chery <nanley.g.chery@intel.com>