mlxsw: spectrum: Simplify port split flow

In commit be94535f ("mlxsw: spectrum: Make split flow match firmware
requirements") we had to modify the port split flow to overcome quirks
in the device's firmware. This resulted in asymmetrical code with
regards to port creation and removal.

The problem in the firmware is long gone and since we can now enforce a
minimal firmware version, we can simplify the code and make it symmetric
again.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>