drm/i915: Remove bitmap tracking for used-pdpes

We only operate on known extents (both for alloc/clear) and so we can use
both the knowledge of the bind/unbind range along with the knowledge of
the existing pagetable to avoid having to allocate temporary and
auxiliary bitmaps.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170215084357.19977-14-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem_gtt.h

@@ -232,9 +232,8 @@ struct i915_page_directory {
 
 struct i915_page_directory_pointer {
 	struct i915_page_dma base;
-
-	unsigned long *used_pdpes;
 	struct i915_page_directory **page_directory;
+	unsigned int used_pdpes;
 };
 
 struct i915_pml4 {