defconfig: enable HAVE_LOW_MEMORY_KILLER on all s[d]m configs

Enable HAVE_LOW_MEMORY_KILLER to avoid premature OOM kills on
all configs for targets that can have a userspace or kernel
lowmemorykiller.

Change-Id: I2ba0148e0fa94ab5903a14c18005f7d550a593fc
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>