net/mlx5: add Direct Rules flow data alloc/free routines

net/mlx5: add Direct Rules flow data alloc/free routines

We are going to share the Direct Rules and Direct Verbs flow
device data structures between master and representors in the
E-Switch configurations over multiport IB device.

The code of initializing and destroying these data is
moved to dedicated routines, this is just a preparation
step for actual data sharing.

Signed-off-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>
Acked-by: Shahaf Shuler <shahafs@mellanox.com>