drm/i915: Only set gem object L3 cache level for IVB devices

Do some further clean up based on the initial review of
drm/i915: Separate cherryview from valleyview.

In this case, in i915_gem_alloc_context_obj() only call
i915_gem_object_set_cache_level() for Ivy Bridge devices
since later platforms don't have L3 control bits in the PTE.

v2: Expand comment to mention snooping requirement. (Ville, Imre)

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Wayne Boyer <wayne.boyer@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1449596332-23470-1-git-send-email-wayne.boyer@intel.com
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

drivers/gpu/drm/i915/i915_gem_context.c

@@ -189,8 +189,15 @@ i915_gem_alloc_context_obj(struct drm_device *dev, size_t size)
 	 * shouldn't touch the cache level, especially as that
 	 * would make the object snooped which might have a
 	 * negative performance impact.
+	 *
+	 * Snooping is required on non-llc platforms in execlist
+	 * mode, but since all GGTT accesses use PAT entry 0 we
+	 * get snooping anyway regardless of cache_level.
+	 *
+	 * This is only applicable for Ivy Bridge devices since
+	 * later platforms don't have L3 control bits in the PTE.
 	 */
-	if (INTEL_INFO(dev)->gen >= 7 && !IS_VALLEYVIEW(dev) && !IS_CHERRYVIEW(dev)) {
+	if (IS_IVYBRIDGE(dev)) {
 		ret = i915_gem_object_set_cache_level(obj, I915_CACHE_L3_LLC);
 		/* Failure shouldn't ever happen this early */
 		if (WARN_ON(ret)) {