ftrace: Clean up function probe methods

When a function probe is created, each function that the probe is
attached to, a "callback" method is called. On release of the probe,
each function entry calls the "free" method.

First, "callback" is a confusing name and does not really match what
it does. Callback sounds like it will be called when the probe
triggers. But that's not the case. This is really an "init" function,
so lets rename it as such.

Secondly, both "init" and "free" do not pass enough information back
to the handlers. Pass back the ops, ip and data for each time the
method is called. We have the information, might as well use it.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>