nfp: flower-ct: add a table to map flow cookies to ct flows

Add a hashtable which contains entries to map flow cookies to ct
flow entries. Currently the entries are added and not used, but
follow-up patches will use this for stats updates and flow deletes.

Signed-off-by: Louis Peens <louis.peens@corigine.com>
Signed-off-by: Yinjun Zhang <yinjun.zhang@corigine.com>
Signed-off-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>