mlxsw: core_linecards: Introduce per line card auxiliary device

mlxsw: core_linecards: Introduce per line card auxiliary device

In order to be eventually able to expose line card gearbox version and
possibility to flash FW, model the line card as a separate device on
auxiliary bus.

Add the auxiliary device for provisioned line card in order to be able
to expose provisioned line card info over devlink dev info. When the
line card becomes active, there may be other additional info added to
the output.

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