drm/i915/gem: Merge GGTT vma flush into a single loop

We only need the one loop to find the dirty vma flush them and their
chipset.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191119100929.2628356-6-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gem/i915_gem_object.c

@@ -279,18 +279,12 @@ i915_gem_object_flush_write_domain(struct drm_i915_gem_object *obj,
 
 	switch (obj->write_domain) {
 	case I915_GEM_DOMAIN_GTT:
-		for_each_ggtt_vma(vma, obj)
-			intel_gt_flush_ggtt_writes(vma->vm->gt);
-
-		intel_frontbuffer_flush(obj->frontbuffer, ORIGIN_CPU);
-
 		for_each_ggtt_vma(vma, obj) {
-			if (vma->iomap)
-				continue;
-
-			i915_vma_unset_ggtt_write(vma);
+			if (i915_vma_unset_ggtt_write(vma))
+				intel_gt_flush_ggtt_writes(vma->vm->gt);
 		}
 
+		intel_frontbuffer_flush(obj->frontbuffer, ORIGIN_CPU);
 		break;
 
 	case I915_GEM_DOMAIN_WC: