We were documenting a bunch of stuff which was removed in commit
93e86b3bc842 ("net: dsa: Remove legacy probing support"). There's some
further cleanup to do in struct dsa_chip_data, so rather than describing
every possible field (when maybe we should be switching to kerneldoc
format), just say what's important about it.
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>