ARM: mvebu: add support for the AXP WiFi AP board

The AXP WiFi AP board is a Marvell platform based on the Armada XP
MV78230 SoC. It has two mini-PCIe connectors, one USB 3.0 port powered
by a USB 3.0 controller on PCIe, two Ethernet ports, 1 GB of RAM, 1 GB
of NAND, 16 MB of SPI flash, one SATA port and one button, two UARTs

Successfully tested: USB 3.0 port, the mini-PCIe connectors, SPI
flash, Ethernet ports, SATA port, button, UART.

Untested: NAND flash, due to lack of mainline support for the Armada
370/XP NAND controller for now.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Tested-by: Seif Mazareeb <seif@marvell.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>