ActivityManagerService: Penalise large apps going to background

Large applications (PSS more than a given threshold) when closed are
penalised with higher ADJ. Now, they will be more prone to be killed by
lowmemorykiller during memory pressure levels. This ensures better app
concurrency and improved subsequent latencies as it leaves some more room
for other smaller bg apps to be alive

Change-Id: I448fa12f55370949b22075595cd75b9c29e5d4b5
lowmemorykiller: Overwrite LMK parameters for low-tier devices

LMK parameters calculated by default algorithm were not optimal for
low-tier devices. Values mentioned here were well tested and
evaluated w.r.t memory and performance for such setups.

Change-Id: I40ed92d204aae6e758028ea1e9bd4ec7226dbe2b