ave Airlie <airlied@redhat.com> 1290396313 +1000

kref: Add a kref_sub function

Makes it possible to optimize batched multiple unrefs.
Initial user will be drivers/gpu/ttm which accumulates unrefs to be
processed outside of atomic code.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
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