Kirkwood: add support for Seagate BlackArmor NAS220

Kirkwood: add support for Seagate BlackArmor NAS220

This patch adds support for Seagate BlackArmor NAS220.

The Seagate BlackArmor NAS 220 is a NAS system based on Marvell 88f6192. It has
32MB NAND and 128MB DRAM. It has two SATA slots, one Gigabit Ethernet port, two
USB 2.0 ports, two buttons and three LEDs. There is a serial port available on
the CN5 connector on the board (1 - TX, 4 - RX, 6 - GND).

The only functionality still not implemented is the bi-color led on the front
panel (status). Pins mpp22 and mpp23 control this led. Setting mpp22 to high and
mpp23 to low results in orange color. Setting mpp22 to low and mpp23 to high
results in blue color.

The third led is wired to show the SATA activity on the two drives.

Signed-off-by: Evgeni Dobrev <evgeni@studio-punkt.com>
Acked-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>