malta: add config file for kernel 3.19.

This is based on config-3.18 with the following changes.

 - CONFIG_GENERIC_NET_UTILS is removed as it is already set in generic
   kernel config.
 - CONFIG_CPU_MICROMIPS is explicitly unset as required in kernel 3.19.

Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@44388 3c298f89-4303-0410-b956-a3cf2f4a3e73