ttm/pool: port to list_lru. (v2)

ttm/pool: port to list_lru. (v2)

This is an initial port of the TTM pools for
write combined and uncached pages to use the list_lru.

This makes the pool's more NUMA aware and avoids
needing separate NUMA pools (later commit enables this).

Cc: Christian Koenig <christian.koenig@amd.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Dave Chinner <david@fromorbit.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>