Adjust lowmemorykiller tunables for Samsung devices

* Set config_lowMemoryKillerMinFreeKbytesAdjust to 8192
* Force all Samsung devices to set 3072 for extra_free_kbytes.
  Default calculation is width * height * 4 * 3 / 1024. This would be 900KB
  for ldpi or 4500KB for hdpi. Let's use 3MB for all devices.

Change-Id: Ib60e478ddd1a64fc2c4abfcdc721041d77615a8d