TTM evicting same-vm bos

[Hellstrom, Thomas]

Hi, Christian

During eviction we want to be able to evict bos that share the VM's
reservation object but that are currently not bound to the VM since
they are not part of the current working set.

TTM can't handle this situation since it's not aware of whether a bo is
bound to a VM or not.

Do you have a preference of how to address this? One idea would be to
forward the operation ctx to the eviction_valuable callback. Another to
add an "unbound" flag to the bo and an "unbound_only" flag to the
operation ctx.

Any feedback appreciated.
Thanks,
Thomas