From now on intel_bb starts tracking added/removed intel_bufs.
We're safe now regardless order of intel_buf close/destroy
or intel_bb destroy paths.

When intel_buf is closed/destroyed first and it was previously added
to intel_bb it calls the code which removes itself from intel_bb.
In destroy path we go over all tracked intel_bufs and clear tracking
information and buffer offset (it is set to INTEL_BUF_INVALID_ADDRESS).

Reset path is handled as follows:
- intel_bb_reset(ibb, false) - just clean objects array leaving
  cache / allocator state intact.
- intel_bb_reset(ibb, true) - purge cache as well as detach intel_bufs
  from intel_bb (release offsets from allocator).

Remove intel_bb_object_offset_to_buf() function as tracking intel_buf
updates (checks for allocator) their offsets after execbuf.

Alter api_intel_bb according to intel-bb changes.

Signed-off-by: Zbigniew Kempczyński <zbigniew.kempczynski@intel.com>
Cc: Dominik Grzegorzek <dominik.grzegorzek@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Petri Latvala <petri.latvala@intel.com>