IB/mlx5: Support adding flow steering rule by raw description

Add support to set a public flow steering rule when its destination is a
TIR by using raw specification data.

The logic follows the verbs API but instead of using ib_spec(s) the raw,
device specific, description is used.

This allows supporting specialty matchers without having to define new
matches in the verbs struct based language.

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