ARM: kirkwood: Add support for NETGEAR ReadyNAS NV+ v2

ARM: kirkwood: Add support for NETGEAR ReadyNAS NV+ v2

Almost all hardware parts of the NETGEAR ReadyNAS NV+ v2 ([1] for more
details) are supported by mainline kernel. The only missing elements in
provided .dts file are:

 - the front LCD module (Winstar WINSTAR WH1602): driver development is
   ongoing. This is the same LCD module as on ReadyNAS 104.
 - the Macronix MX25L512 512Kbit SPI flash: no time to play with it yet.

The device is the big brother (4 vs 2 bay) of the ReadyNAS Duo v2. The
main differences are some additional LEDs for the disks, a Marvell
88SM4140 SATA Port multiplier (no driver required to access the disk)
and previously described LCD module. Otherwise, it shares the same SoC
(kirkwood 88F6282), RAM (256MB), NAND (128MB), RTC chip (Ricoh rs5c372a),
fan controller (GMT G762), XHCI controller (NEC/Renesas µPD720200).

[1]: http://natisbad.org/NAS5/

Signed-off-by: Arnaud Ebalard <arno@natisbad.org>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>