kirkwood: add support for Iomega Storcenter ix4-200d

kirkwood: add support for Iomega Storcenter ix4-200d

Iomega Storcenter ix4-200d is a four-bay SATA NAS powered by a Marvell
Kirkwood SoC clocked at 1.2GHz. It has 512MB of RAM and 32MB of
flash memory, 3x USB 2.0 and 2x 1Gbit/s NIC

Specification:
- SoC: Marvell Kirkwood 88F6281
- CPU/Speed: 1200Mhz
- Flash size: 32 MiB
- RAM: 512MB
- LAN: 2x 1Gbit/s
- 3x USB 2.0

Notes:
- The blue drive LED is triggered by HDD activity, it can not be controlled
  via GPIO.
- The LCD screen requires proprietary code and does not function at this time.
- Due to a kernel-related issue with the Marvell 88SE6121 SATA controller,
  currently only trays numbered #3 and #4 work, #1 and #2 do not. [1]

Serial pinout:

    CN4
    --------------
    | 10 8 6 4 2 |
    |  9 7 5 3 1 |
    -------------- PIN 1 Mark (fat line)

     1 = RXD
     4 = TXD
     6 = GND
     9 = 3.3V (not necessary to connect)

Installation instructions:
1. download initramfs-uImage and copy into tftp server
2. connect the tftp server to network port #1
3. access uboot environment with serial cable and run

    setenv mainlineLinux yes
    setenv arcNumber 1682
    setenv console 'console=ttyS0,115200n8'
    setenv mtdparts 'mtdparts=orion_nand:0x100000@0x000000(u-boot)ro,0x20000@0xA0000(u-boot environment)ro,0x300000@0x100000(kernel),0x1C00000@0x400000(ubi)'
    setenv bootargs_root 'root='
    setenv bootcmd 'setenv bootargs ${console} ${mtdparts} ${bootargs_root}; nand read.e 0x800000 0x100000 0x300000; bootm 0x00800000'
    saveenv
    setenv serverip 192.168.1.1
    setenv ipaddr 192.168.1.2
    tftpboot 0x00800000 [initramfs-uImage filename]
    bootm 0x00800000

4. connect to LAN on network port #2, log into openwrt and sysupgrade to install into flash

[1] https://bugzilla.kernel.org/show_bug.cgi?id=216094

Signed-off-by: Sander van Deijck <sander@vandeijck.com>
(aligned FROM from signed-off. LED+key rename, whitespace removal)
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>