[ARM] 4766/2: ixp4xx: Update ixp4xx_defconfig, enabling all supported boards

This updates the defconfig for the ixp4xx machine in arch/arm/config
taking all the defaults, with the following additions:

1) Enable support for the nslu2, loft, gateway7001, wg302v2,
   dsmg600, and gtwx5715 boards.
2) Enable EABI, OABI, HOTPLUG and FW_LOADER.
3) Enable the RTC subsystem, with drivers for the RTC chips on the
   nslu2 (x1205) and nas100d/dsmg600 (pcf8563) boards.
4) Enable the LEDS subsystem to support the nslu2, nas100d and
   dsmg600 boards.  Enable the ixp4xx beeper driver.
5) Enable the USB subsystem, USB host driver support and USB mass
   storage support (required for boot disk on nslu2 board).
6) Enable the ATA subsystem, with drivers for the nas100d/dsmg600
   (pata_artop) and avila (ixp4xx_cf) boards.
Signed-off-by: NRod Whitby <rod@whitby.id.au>
Acked-by: NLennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>