ARM: mvebu: Add Armada 388 General Purpose Development Board support

The A388-GP is a board produced by Marvell that holds

- 1 PCIe slot
- 2 mini PCIe slot (one of them is multiplexed with the PCIe slot,
  muxing is selected through the GPIO expander)
- 1 16MB SPI-NOR
- 2 Gigabit Ethernet ports
- 4 SATA ports (2 of them are multiplexed with the mini PCIe slots,
  muxing is selected through the GPIO expander)
- 1 SDIO slot
- 1 USB3 port
- 2 USB2 port
- 2 GPIO/interrupts expander on I2C

Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>