drm/i915: Store number of active engines in device info

Until now code was calling hweight32 to figure out the
number from device_info->ring_mask at runtime. Instead
we can cache it at engine init time and use directly.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Dave Gordon <david.s.gordon@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1470842530-35854-1-git-send-email-tvrtko.ursulin@linux.intel.com
diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index ade2446..2a3d6d2 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -3226,7 +3226,7 @@
 	struct drm_device *dev = node->minor->dev;
 	struct drm_i915_private *dev_priv = to_i915(dev);
 	struct intel_engine_cs *engine;
-	int num_rings = hweight32(INTEL_INFO(dev)->ring_mask);
+	int num_rings = INTEL_INFO(dev)->num_rings;
 	enum intel_engine_id id;
 	int j, ret;