tracing/function-graph-tracer: make set_graph_function file support ftrace regex

Impact: trace only functions matching a pattern

The set_graph_function file let one to trace only one or several
chosen functions and follow all their code flow.

Currently, only a constant function name is allowed so this patch
allows the ftrace_regex functions:

- matches all functions that end with "name":
  echo *name > set_graph_function

- matches all functions that begin with "name":
  echo name* > set_graph_function

- matches all functions that contains "name":
  echo *name* > set_graph_function

Example:

echo mutex* > set_graph_function

 0)               |  mutex_lock_nested() {
 0)   0.563 us    |    __might_sleep();
 0)   2.072 us    |  }
 0)               |  mutex_unlock() {
 0)   1.036 us    |    __mutex_unlock_slowpath();
 0)   2.433 us    |  }
 0)               |  mutex_unlock() {
 0)   0.691 us    |    __mutex_unlock_slowpath();
 0)   1.787 us    |  }
 0)               |  mutex_lock_interruptible_nested() {
 0)   0.548 us    |    __might_sleep();
 0)   1.945 us    |  }

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>