kernel: backport ARM memset fixes for GCC 4.7/4.8

Now that GCC 4.8 is the default, make sure that we have the relevant
memset fixes to avoid nasty kernel crashes.

Signed-off-by: Florian Fainelli <florian@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@39902 3c298f89-4303-0410-b956-a3cf2f4a3e73
gpio-button-hotplug: don't build for 3.3 kernels

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