ftrace: fix dynamic ftrace selftest

With the adding of the configuration changes in the Makefile to prevent
tracing of functions in the ftrace code, all tracing of all the ftrace
code has been removed. Unfortunately, one of the selftests, relied on
a function to be traced. With the new change, the function was no longer
traced and the test failed.

This patch separates out the test function into its own file so that
we can add the "-pg" flag to the compilation of that function and the
adding of the mcount call to that function.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>