arm: Allow saving of stacktraces from other processes

Currently, a process is only able to save its own stacktrace
due to concerns about other processes going away while the
saving is occuring. Realistaically though, hititng this
case is very unlikely and the debugging benefit outweighs
the risk. Enable saving of other stacktraces for access
through systems such as procfs.

Change-Id: I584388f6edb48431bfec8d11d217f0fdc116f73e
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
Signed-off-by: Darescu Ionut <johnny@esi.ro>