net/mlx5_core: Introduce flow steering API

Introducing the following objects:

mlx5_flow_root_namespace: represent the root of specific flow table
type tree(e.g NIC receive, FDB, etc..)

mlx5_flow_group: define the mask of the flow specification.

fs_fte(flow steering flow table entry): defines the value of the
flow specification.

The following describes the relationships between the tree objects:
root_namespace --> priorities -->namespaces -->
priorities -->flow-tables --> flow-groups -->
flow-entries --> destinations

When we create new object(flow table/flow group/flow table entry), we
call to the FW command and then we add the related sw object to the tree.

When we destroy object, e.g. call to mlx5_destroy_flow_table, we use
the tree node destructor for destroying the FW object and remove the
node from the tree.

Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Moni Shoua <monis@mellanox.com>
Signed-off-by: Matan Barak <matanb@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>