net/ixgbe/base: add EEE support for some PHYs

net/ixgbe/base: add EEE support for some PHYs

This patch adds Energy Efficient Ethernet (EEE) support for
some Marvell PHYs on some future platforms.
Because EEE capability or status was not indicated previously,
this patch simply assumes that it is supported.

As soon as there is a PHY that does not support EEE, there will
be defects in this area because the driver will not report the
EEE status correctly.

This also deletes some now-unused definitions from an earlier
Marvell PHY implementation and combines a device ID check into a
switch statement.

Signed-off-by: Wei Dai <wei.dai@intel.com>