phy: marvell: phy-mvebu-cp110-comphy: implement RXAUI support

Marvell's cp110 phy supports RXAUI on lanes 2, 3, 4, and 5 when
connected to port zero. When used in this mode, lanes operate in pairs
of two (2 and 3, 4 and 5).

Signed-off-by: Matt Pelland <mpelland@starry.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>