mcs814x: enable POSIX file locking

opkg (and possible other tools) are currently broken as it requires
file locking support enabled in the kernel.
Without this results in a message like:

root@OpenWrt:/etc/config# opkg update
Collected errors:
 * opkg_conf_load: Could not lock /var/lock/opkg.lock: Permission denied.

With this patch opkg is fully functional on this platform.

Signed-off-by: Michael Heimpold <mhei@heimpold.de>
Signed-off-by: Florian Fainelli <florian@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@37745 3c298f89-4303-0410-b956-a3cf2f4a3e73