drm/i915: Remove bitmap tracking for used-ptes

drm/i915: Remove bitmap tracking for used-ptes

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.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99295
Signed-off-by: Chris Wilson <[email protected]>
Reviewed-by: Matthew Auld <[email protected]>
Reviewed-by: Michał Winiarski <[email protected]>
Link: http://patchwork.freedesktop.org/patch/msgid/[email protected]