Add basic support for the Marvell 88X2222 multi-speed ethernet
transceiver.

This PHY provides data transmission over fiber-optic as well as Twinax
copper links. The 88X2222 supports 2 ports of 10GBase-R and 1000Base-X
on the line-side interface. The host-side interface supports 4 ports of
10GBase-R, RXAUI, 1000Base-X and 2 ports of XAUI.

This driver, however, supports only XAUI on the host-side and
1000Base-X/10GBase-R on the line-side, for now. The SGMII is also
supported over 1000Base-X. Interrupts are not supported.

Internal registers access compliant with the Clause 45 specification.
Signed-off-by: Ivan Bornyakov <i.bornyakov@metrotek.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>