net/mlx5_core: Flow steering tree initialization

Flow steering initialization is based on static tree which
illustrates the flow steering tree when the driver is loaded. The
initialization considers the max supported flow table level of the device,
a minimum of 2 kernel flow tables(vlan and mac) are required to have
kernel flow table functionality.

The tree structures when the driver is loaded:

		root_namespace(receive nic)
			  |
		priority-0 (kernel priority)
			  |
		namespace(kernel namespace)
			  |
		priority-0 (flow tables priority)

In the following patches, When the EN driver will use the flow steering
API, it create two flow tables and their flow groups under
priority-0(flow tables priority).

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>