mvebu: initial support for Marvell Armada 3720 DB board

mvebu: initial support for Marvell Armada 3720 DB board

Add initial support for Marvell Armada cortex-a53 based
DB-88F3720-DDR3-Modular development board.

Specifications:
- Dual core ARMv8 Cortex-A53 CPU (up to 1.0 GHz)
- 4Gb 16-bit DDR3/3L DRAM memory
- 128Mb SPI NOR flash memory
- 8Gb eMMC NAND flash memory
- 1 x SATA Rev 3.0 port
- 1 x PCI Express (PCIe) Gen 2.0 or 1 x mini PCI Express (PCIe) Gen 2.0
- 1 x 1G Ethernet port via RGMII (RJ45)
- 1 x SD card port
- 1 x USB3 (USB2 backward) host\device port via type C connector
- 1 x USB2 host port via type A connector
- 1 x serial COM port driven by the 88F3720 UART interface and converted to
  USB via FTDI IC (option to connect the UART DB9 adapter)
- I2C Master Interface:
  - 1 x EEPROM @ address 0x57
  - 1 x I/O Expanders @ address 0x22
  - Sample at Reset (SatR) memory device @ address 0x4C
  - RTC clock generator PT7C4337AWE @ address 0x68
  - USB3 switch PI5USB30213XEA @ address 0x0D
  - ID component of PHY module @ address 0x24
- 1 x JTAG interface for CPU emulator
- 1 x SETM and JTAG debug interface
- 1 x power connector for HDD supply
- 1 x 12V DC jack power connector
- Board dimensions: 150 mm x 179 mm
- LED interface for system status

Booting from SD card:
 1. reset U-Boot environment:
      env default -a
      saveenv

 2. prepare U-Boot with boot script:
      setenv bootcmd "load mmc 0:1 0x4d00000 boot.scr; source 0x4d00000"
      saveenv

    or manually:
      setenv fdt_name armada-3720-db.dtb
      setenv image_name Image
      setenv bootcmd 'mmc dev 0; ext4load mmc 0:1 $kernel_addr $image_name;ext4load mmc 0:1 $fdt_addr $fdt_name;setenv bootargs $console root=/dev/mmcblk1p2 rw rootwait; booti $kernel_addr - $fdt_addr'
      saveenv

Signed-off-by: Damir Samardzic <damir.samardzic@sartura.hr>
(backported from 322a02f66607be5fa774f9187003631494bc2809)