Memory Resource Controller no longer depends on Resource counters since
Kernel version 4.0.
3.18 is the only still supported version needing Resource counters for
MEMCG, thus declare the dependency only for that version.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@46024 3c298f89-4303-0410-b956-a3cf2f4a3e73