net: dsa: ocelot: document why reset procedure is different for felix/seville

The overall idea (issue soft reset, enable memories, initialize
memories, enable core) is the same, so it would make sense that an
attempt is made to unify the procedures.

It is not immediately obvious that the fields are not part of the same
register targets, though. So add a comment.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>