net/mlx5: E-Switch, Move representors definition to a global scope

In preparation for IB representors, move representors structs to a global
scope, also expose functions needed for registration, unregistration,
eswitch mode and creating a flow rule to direct traffic from SQs to the
right VF.

Signed-off-by: Mark Bloch <markb@mellanox.com>
Reviewed-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>