tracing: use macros to create internal ftrace entry ring buffer structures

The entries used by ftrace internal code (plugins) currently have their
formats manually exported to userspace. That is, the format files in
debugfs/tracing/events/ftrace/*/format are currently created by hand.
This is a maintenance nightmare, and can easily become out of sync
with what is actually shown.

This patch uses the methodology of the TRACE_EVENT macros to build
the structures so that their formats can be automated and this
will keep the structures in sync with what users can see.

This patch only changes the way the structures are created. Further
patches will build off of this to automate the format files.

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