drm/i915: move bsd dispatch index somewhere better

Adding stuff at the bottom is really no how this should be done, since
that's the place for ums/dri dungeons.

This was added in

commit a8ebba75b358f9c912cbcba0c14a2072e7280b2f
Author: Zhao Yakui <yakui.zhao@intel.com>
Date:   Thu Apr 17 10:37:40 2014 +0800

    drm/i915: Use the coarse ping-pong mechanism based on drm fd to dispatch the BSD command on BDW GT3

Also add a note to prevent this from happening again - people really
should be less lazy and take more time to look for a good home of
their new driver-global state.

Cc: Imre Deak <imre.deak@intel.com>
Cc: Zhao Yakui <yakui.zhao@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 94e53a0..de2fd90 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -1027,12 +1027,12 @@
 		int ring_id;
 
 		mutex_lock(&dev->struct_mutex);
-		if (dev_priv->ring_index == 0) {
+		if (dev_priv->mm.bsd_ring_dispatch_index == 0) {
 			ring_id = VCS;
-			dev_priv->ring_index = 1;
+			dev_priv->mm.bsd_ring_dispatch_index = 1;
 		} else {
 			ring_id = VCS2;
-			dev_priv->ring_index = 0;
+			dev_priv->mm.bsd_ring_dispatch_index = 0;
 		}
 		file_priv->bsd_ring = &dev_priv->ring[ring_id];
 		mutex_unlock(&dev->struct_mutex);