drm/ttm: Fix memory type compatibility check

commit 59c8e66378fb78adbcd05f0d09783dde6fef282b upstream.

Also check the busy placements before deciding to move a buffer object.
Failing to do this may result in a completely unneccessary move within a
single memory type.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Jakob Bornecrantz <jakob@vmware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>