kernel: add missing config symbol for 3.10

Signed-off-by: Jonas Gorski <jogo@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@37123 3c298f89-4303-0410-b956-a3cf2f4a3e73
ixp4xx: add support for linux 3.10

Run tested on a NSLU2.

Signed-off-by: Jonas Gorski <jogo@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@37124 3c298f89-4303-0410-b956-a3cf2f4a3e73