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>

src/intel/vulkan/gen7_cmd_buffer.c

@@ -260,6 +260,13 @@ genX(cmd_buffer_flush_dynamic_state)(struct anv_cmd_buffer *cmd_buffer)
    cmd_buffer->state.dirty = 0;
 }
 
+void
+genX(cmd_buffer_enable_pma_fix)(struct anv_cmd_buffer *cmd_buffer,
+                                bool enable)
+{
+   /* The NP PMA fix doesn't exist on gen7 */
+}
+
 void genX(CmdSetEvent)(
     VkCommandBuffer                             commandBuffer,
     VkEvent                                     event,