Always invalidate on lock (even for write). This ensures that partial tile
writes will not overwrite buffer with dummy data from previously prefetched lines.
On subsequent lock calls, in case of write, update direction to bi_directional.
This way buffer will get flushed during unlock.
Change-Id: If3f1deffefe14af1dbdb2dae0a77b25106d35e5c
Signed-off-by: Amol Jadi <quic_ajadi@quicinc.com>