mlxsw: spectrum: Make split flow match firmware requirements

When a port is created following a split / unsplit we need to map it to
the correct module and lane, enable it and then continue to initialize
its various parameters such as MTU and VLAN filters.

Under certain conditions, such as trying to split ports at the bottom
row of the front panel by four, we get firmware errors.

After evaluating this with the firmware team it was decided to alter the
split / unsplit flow, so that first all the affected ports are mapped,
then enabled and finally each is initialized separately.

Fix the split / unsplit flow by first mapping and enabling all the
affected ports. Newer firmware versions will support both flows.

Fixes: 18f1e70c ("mlxsw: spectrum: Introduce port splitting")
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>