mlxsw: minimal: Extend module to port mapping with slot index

The interfaces for ports found on line card are created and removed
dynamically after line card is getting active or inactive.

Introduce per line card array with module to port mapping.
For each port get 'slot_index' through PMLP register and set port
mapping for the relevant [slot_index][module] entry.

Split module and port allocation into separate routines.

Split per line card port creation and removing into separate routines.
Motivation to re-use these routines for line card operations.

Signed-off-by: Vadim Pasternak <vadimp@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>