mlxsw: reg: Extend MDDQ by device_info

Extend existing MDDQ register by possibility to query information about
devices residing on a line card.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>