mm/oom-kill: Add option to panic when killing foreground app

This setting is useful to debug memory intensive test scenarios,
which are close to the limit of what the device supports.

Change-Id: Id09f43736bd3c9586b4dac4fae570e78089f5bb3
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>
[cgoldswo@codeaurora.org: Add macro introduced in obsolete patch]
Signed-off-by: Chris Goldsworthy <cgoldswo@codeaurora.org>