Merge branch 'mlxsw-Make-port-split-code-more-generic'

Ido Schimmel says:

====================
mlxsw: Make port split code more generic

Jiri says:

Currently, we assume some limitations and constant values which are not
applicable for Spectrum-3 which has 8 lanes ports (instead of previous 4
lanes).

This patch does 2 things:

1) Generalizes the code to not use constants so it can work for 4, 8 and
   possibly 16 lanes.

2) Enforces some assumptions we had in the code but did not check.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>