Basic KSM Support

[ported from ics commit]

Be sure to add '#define MADV_MERGEABLE 12' to
bionic/libc/include/sys/mman.h so we can have a central place for this

parse the process memory map and inform madvise common HEAP/Stack
regions on fork from zygote

These then can be used by the kernel KSM module to re-join (copy on write)
pages between the various dalvik processes.

As is on a fully loaded system you can expect ~12MB to be indicated to be
scanned by KSM.. of this 10-15% will be saved; as such a recommend a very
slow scan until as any logic to stop scanning while sleeping will require
another process and remove all memory savings provided by this logic.

To activate on a KSM kernel (2min for full scan of ~16m and 1%CPU):

echo 4000 > /sys/kernel/mm/ksm/sleep_millisecs
echo 128 > /sys/kernel/mm/ksm/pages_to_scan
echo 1 > /sys/kernel/mm/ksm/run

Newer kernels only require the last line.

In future additional memory regions and kernel logic may improve this.

Change-Id: If431bf77a21bc7358499678f83d84404e5db2738