RDMA/mlx5: Refactor flow action parsing to be more generic

Make the parsing of flow actions more generic so it could be used by
mlx5 raw create flow.

Signed-off-by: Mark Bloch <markb@mellanox.com>
Reviewed-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>