staging: android: lowmemorykiller: Add config option to support oom_adj values

The conversion to use oom_score_adj instead of the deprecated oom_adj
values breaks existing user-space code. Add a config option to convert
oom_adj values written to oom_score_adj values if they appear to be
valid oom_adj values.

Change-Id: I68308125059b802ee2991feefb07e9703bc48549
Signed-off-by: Arve Hjønnevåg <arve@android.com>