devlink: add generic info version names

Add defines and docs for generic info versions.

v3:
 - add docs;
 - separate patch (Jiri).

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>