selftests/ftrace: multiple_kprobes: Also check for support

The multiple_kprobes test case fails to check for KPROBE_EVENT support.
Add the check to prevent a false test result.
Signed-off-by: Thomas Meyer <thomas@m3y3r.de>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>

tools/testing/selftests/ftrace/test.d/kprobe/multiple_kprobes.tc

 #!/bin/sh
 # description: Register/unregister many kprobe events
 
+[ -f kprobe_events ] || exit_unsupported # this is configurable
+
 # ftrace fentry skip size depends on the machine architecture.
 # Currently HAVE_KPROBES_ON_FTRACE defined on x86 and powerpc64le
 case `uname -m` in