net: dsa: mv88e6xxx: enable SerDes PCS register dump via ethtool -d on Topaz

Commit bf3504ce

 ("net: dsa: mv88e6xxx: Add 6390 family PCS
registers to ethtool -d") added support for dumping SerDes PCS registers
via ethtool -d for Peridot.

The same implementation is also valid for Topaz, but was not
enabled at the time.

Signed-off-by: Marek Behún <kabel@kernel.org>
Fixes: bf3504ce

 ("net: dsa: mv88e6xxx: Add 6390 family PCS registers to ethtool -d")
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>