kernel: add missing KEEP() statements for gc-sections patch in 3.18

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@43405 3c298f89-4303-0410-b956-a3cf2f4a3e73
cns3xxx: add experimental 3.18 support

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@43406 3c298f89-4303-0410-b956-a3cf2f4a3e73
mt76: fix a compile error on 3.18

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@43407 3c298f89-4303-0410-b956-a3cf2f4a3e73