phy: marvell: a3700: Use comphy_mux on Armada 37xx.

Lane 0 supports SGMII1 and USB3.
Lane 1 supports SGMII0 and PEX0.
Lane 2 supports SATA0 and USB3.

This is needed for Armada 37xx.

This introduces new device tree bindings. AFAIK there is currently no
driver for Armada 37xx comphy in Linux. When such a driver will be
pushed into Linux, this will need to be rewritten accordingly.

Signed-off-by: Marek Behun <marek.behun@nic.cz>
Signed-off-by: Stefan Roese <sr@denx.de>