tracing: Add SPDX license GPL-2.0 license identifier to inter-event testcases

Apparently this directory was missed in the license cleanup process -
add the missing identifiers to the trigger/inter-event test cases.

Link: http://lkml.kernel.org/r/6f9828c2cfb0b378ebd217a39a1b44f063fc17fb.1550100284.git.tom.zanussi@linux.intel.com



Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>