crash: port ps command

I believe that this is complete. The implementation of -s is terrible;
it does a full stack trace just to get the initial stack pointer, but we
can optimize that later.

Co-authored-by: YassineLr <[email protected]>
Signed-off-by: YassineLr <[email protected]>
Signed-off-by: Omar Sandoval <[email protected]>

Author: osandov