[ARM] 4772/2: ixp4xx: Register nslu2 rtc i2c_board_info

Register the i2c board info related to the RTC chip on the nslu2 board
to allow it to be found automatically on boot.

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