ARM: kirkwood: add SBx81LIFXCAT board

This is a series of line cards for Allied Telesis's SBx8100 chassis
switch. The CPU block is common to the SBx81GP24 and SBx81GT24 cards
cards collectively referred to as SBx81LIFXCAT in u-boot.

Signed-off-by: Chris Packham <judge.packham@gmail.com>
Signed-off-by: Stefan Roese <sr@denx.de>