Fix some oom tuning and display size stuff.

Fix a problem where we would not respect the device's
override display density/size if those had been reset at
some point (to an empty string).

Tweak the tuning of low RAM devices to consider 480x800 as
the base line resolution.  That is our target these days.

Improve output of oom and meminfo to include this tuning
information.

Change-Id: Ic9a85b0391b075178c4ac17e64086ef21889f430