[ARM] 4874/2: ixp4xx: Add support for the Freecom FSG-3 board

The Freecom-FSG3 is a small network-attached-storage device with the
following feature set:

* Intel IXP422
* 4MB Flash (ixp4xx flash driver)
* 64MB RAM
* 4 USB 2.0 host ports (ehci and ohci drivers)
* 1 WAN (eth1) and 3 LAN (eth0) ethernet ports
  * Supported by the open source ixp4xx ethernet driver
* Via VT6421 disk controller (libata and sata-via drivers)
  * Internal hard disk (PATA supported, SATA not yet supported)
  * External SATA port (not yet supported)
* ISL1208 RTC chip
* Winbond 83782 temp sensor and fan controller
* MiniPCI slot

The ixp4xx_defconfig is also updated to support this device (the
leds-fsg driver is to be submitted separately via the leds tree after
this initial support is merged, as it depends on header gpio defines).

Signed-off-by: Rod Whitby <rod@whitby.id.au>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>