selftests/ftrace: Add function profiling stat testcase

Add a testcase for function profiling per-cpu statistics
interface. There is already func_profile.tc, but that is
mainly focusing on the combination of function-profiler
and function tracer. This testcase ensures trace_stat
per-cpu function statistics is correctly updated.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Shuah Khan (Samsung OSG) <shuah@kernel.org>