Support halt the trace when schd-dbg hit deadline

Usage:

start atrace as usual:
>atrace --async_start sched freq ...

then use schd-dbg with -trace arguments
./schd-dbg -trace -deadline_us 2500

This makes schd-dbg to stop trace once it detects a transaction
duration over the deadline. By writing '0' to
/sys/kernel/debug/tracing and halt the process. The tracelog is
then available on /sys/kernel/debug/trace

Bug: b/36669012
Test: sailfish with prebuilt kernel
Change-Id: I9f81109cd22705f070f3f78ddf3539b8fa1f9973