Introduce flow steering matcher object and its create and destroy methods.

This matcher object holds some mlx5 specific driver properties that
matches the underlay device specification when an mlx5 flow steering group
is created.

It will be used in downstream patches to be part of mlx5 specific create
flow method.
Signed-off-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>