3.3 kernels do not have the required changes which would make
gpio-button-hotplug work, disallow building on those kernels for now.
Signed-off-by: Florian Fainelli <florian@openwrt.org>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@39903 3c298f89-4303-0410-b956-a3cf2f4a3e73