selftests: ftrace: add more config fragments

We need to enable more configs to make test more
without this patch,we got lots of "UNSUPPORTED"

before the patch:
http://pastebin.ubuntu.com/25784377/
after the patch:
http://pastebin.ubuntu.com/25784387/

Signed-off-by: Lei Yang <Lei.Yang@windriver.com>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>

tools/testing/selftests/ftrace/config

@@ -1,2 +1,6 @@
 CONFIG_KPROBES=y
 CONFIG_FTRACE=y
+CONFIG_FUNCTION_PROFILER=y
+CONFIG_TRACER_SNAPSHOT=y
+CONFIG_STACK_TRACER=y
+CONFIG_HIST_TRIGGERS=y