mvebu: add support for Buffalo LinkStation LS220DE

mvebu: add support for Buffalo LinkStation LS220DE

The Buffalo LinkStation LS220DE is a dual bay NAS, based on Marvell
Armada 370

Hardware:
   SoC:         Marvell Armada 88F6707
   CPU:         Cortex-A9 800 MHz, 1 core
   Flash 1:     SPI-NOR 1 MiB (U-Boot)
   Flash 2:     NAND 512 MiB (OS)
   RAM:         DDR3 256 MiB
   Ethernet:    1x 1GbE
   USB:         1x 2.0
   SATA:        2x 3Gb/s
   LEDs/Input:  5x / 2x (1x button, 1x slide-switch)
   Fan:         1x casing

Flash instructions, from hard drive:
  1. Get access to the "boot" partition at the hard drive where the stock
     firmware is installed. It can be done with acp-commander or by
     plugging the hard drive to a computer.
  2. Backup the stock uImage:
         mv /boot/uImage.buffalo /boot/uImage.buffalo.bak
  3. Move and rename the Openwrt initramfs image to the boot partition:
         mv openwrt-initramfs-kernel.bin /boot/uImage.buffalo
  4. Power on the Linkstation with the hardrive inside. Now Openwrt will
     boot, but still not installed.
  5. Connect via ssh to OpenWrt:
         ssh root@192.168.1.1
  6. Rename boot files inside boot partition
         mount -t ext3 /dev/sda1 /mnt
         mv /mnt/uImage.buffalo /mnt/uImage.buffalo.openwrt.bak
         mv /mnt/initrd.buffalo /mnt/initrd.buffalo.bak
  7. Format ubi partitions at the NAND flash ("kernel_ubi" and "ubi"):
         ubiformat /dev/mtd0 -y
         ubidetach -p /dev/mtd1
         ubiformat /dev/mtd1 -y
  8. Flash the sysupgrade image:
         sysupgrade -n openwrt-squashfs-sysupgrade.bin
  9. Wait until it finish, the device will reboot with OpenWrt installed
     on the NAND flash.

Restore the stock firmware:
  1. Take the hard drive used for the installation and restore boot backup
     files to their original names:
         mount -t ext3 /dev/sda1 /mnt
         mv /mnt/uImage.buffalo.bak /mnt/uImage.buffalo
         mv /mnt/initrd.buffalo.bak /mnt/initrd.buffalo
  2. Boot from the hard drive and perform a stock firmware update using
     the Buffalo utility. The NAND will be restored to the original
     state.

Signed-off-by: Daniel González Cabanelas <dgcbueu@gmail.com>