kirkwood: add support for Seagate BlackArmor NAS220

kirkwood: add support for Seagate BlackArmor NAS220

The Seagate BlackArmor NAS220 is a consumer NAS
with two internal drive bays. The stock OS runs
RAID 1 over the disks via mdadm.

Device specification:
- SoC: Marvell 88F6192 800 MHz
- RAM: 128 MB
- Flash: 32 MB
- 2 x internal SATA II drives
- Ethernet: 10/100/1000 Mbps (single port, no switch)
- WLAN: None
- LED: Power, Status, Sata Activity
- Key: Power, Reset
- Serial: 10 pin header, (115200,8,N,1), 3.3V TTL
	9|x  -   x|10
	7|x  -   x|8
	5|x  - GND|6
	3|x  -  RX|4
	1|TX -   x|2
	front of case
- USB ports: 2 x USB 2.0

Flash instruction:

NOTE: this process uses a serial connection. It will upgrade the
bootloader and reset the bootloader environment variables

TFTP server setup
- Setup PC with TFTP server set the PC IP to 10.4.50.5 as TFTP server
- Copy these files to TFTP server location
    - u-boot.kwb
    - seagate_blackarmor-nas220-initramfs-uImage
    - seagate_blackarmor-nas220-squashfs-sysupgrade.bin
    - seagate_blackarmor-nas220-squashfs-factory.bin

Seagate NAS setup
- Connect LAN cable between PC and seagate device
- Connect to serial to seagate device

Install u-boot
- Boot seagate device and stop in bootloader by pressing any key
- run 'printenv' from u-boot and save the values
- tftpboot 0x2000000 u-boot.kwb
- nand erase.part uboot
- nand write 0x2000000 0x0 ${filesize}
- reset

Update MAC address in u-boot env
- Stop in u-boot by pressing any key
- Get your MAC address from your saved printenv. Is also on chassis
- setenv ethaddr <your MAC>
- saveenv

Option 1 (recommended) - Install OpenWrt via initramfs and sysupgrade
- tftpboot 0x2000000 seagate_blackarmor-nas220-initramfs-uImage
- bootm 0x2000000
- *OpenWrt should be running now, however it is not written to flash yet*
- From the running instance of OpenWrt use Luci's "flash image" feature
    from the web site or use sysupgrade from the console to write
    seagate_blackarmor-nas220-squashfs-sysupgrade.bin to flash

Option 2 - Install OpenWrt by flashing factory image from u-boot
- nand erase.part ubi
- tftpboot 0x2000000 seagate_blackarmor-nas220-squashfs-factory.bin
- nand write 0x2000000 ubi ${filesize}
- reset

Signed-off-by: Kip Porterfield <kip.porterfield@gmail.com>