Merge branch 'mv88e6xxx-Add-SERDES-PCS-registers-to-ethtool-dump'

Andrew Lunn says:

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mv88e6xxx: Add SERDES/PCS registers to ethtool -d

ethtool -d will dump the registers of an interface. For mv88e6xxx
switch ports, this dump covers the port specific registers. Extend
this with the SERDES/PCS registers, if a port has a SERDES.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>