drm/i915: Introduce for_each_ring() macro

In many places we wish to iterate over the rings associated with the
GPU, so refactor them to use a common macro.

Along the way, there are a few code removals that should be side-effect
free and some rearrangement which should only have a cosmetic impact,
such as error-state.

Note that this slightly changes the semantics in the hangcheck code:
We now always cycle through all enabled rings instead of
short-circuiting the logic.

v2: Pull in a couple of suggestions from Ben and Daniel for
intel_ring_initialized() and not removing the warning (just moving them
to a new home, closer to the error).

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
[danvet: Added note to commit message about the small behaviour
change, suggested by Ben Widawsky.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index f0763f2..d3e1948 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -893,15 +893,15 @@
 	 */
 	if (drm_core_check_feature(dev, DRIVER_MODESET) ||
 			!dev_priv->mm.suspended) {
+		struct intel_ring_buffer *ring;
+		int i;
+
 		dev_priv->mm.suspended = 0;
 
 		i915_gem_init_swizzling(dev);
 
-		dev_priv->ring[RCS].init(&dev_priv->ring[RCS]);
-		if (HAS_BSD(dev))
-		    dev_priv->ring[VCS].init(&dev_priv->ring[VCS]);
-		if (HAS_BLT(dev))
-		    dev_priv->ring[BCS].init(&dev_priv->ring[BCS]);
+		for_each_ring(ring, dev_priv, i)
+			ring->init(ring);
 
 		i915_gem_init_ppgtt(dev);