net/mlx5: IPsec: Add HW crypto offload support

This patch adds support for Connect-X IPsec crypto offload
by implementing the IPsec acceleration layer needed routines,
which delegates IPsec offloads to Connect-X routines.

In Connect-X IPsec, a Security Association (SA) is added or deleted
via allocating a HW context of an encryption/decryption key and
a HW context of a matching SA (IPsec object).
The Security Policy (SP) is added or deleted by creating matching Tx/Rx
steering rules whith an action of encryption/decryption respectively,
executed using the previously allocated SA HW context.

When new xfrm state (SA) is added:
- Use a separate crypto key HW context.
- Create a separate IPsec context in HW to inlcude the SA properties:
 - aes-gcm salt.
 - ICV properties (ICV length, implicit IV).
 - on supported devices also update ESN.
 - associate the allocated crypto key with this IPsec context.

Introduce a new compilation flag MLX5_IPSEC for it.

Downstream patches will implement the Rx,Tx steering
and will add the update esn.

Signed-off-by: Raed Salem <raeds@mellanox.com>
Signed-off-by: Huy Nguyen <huyn@mellanox.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>