tracing: Add DEFINE_EVENT(), DEFINE_SINGLE_EVENT() support to docbook

The introduction of the new 'DECLARE_EVENT_CLASS()' obviates the
need for the 'TRACE_EVENT()' macro in some cases. Thus, docbook
style comments that used to live with 'TRACE_EVENT()' are now
moved to 'DEFINE_EVENT()'. Thus, we need to make the docbook
system understand the new 'DEFINE_EVENT()' macro. In addition
I've tried to futureproof the patch, by also adding support for
'DEFINE_SINGLE_EVENT()', since there has been discussion about
renaming: TRACE_EVENT() -> DEFINE_SINGLE_EVENT().

Without this patch the tracepoint docbook fails to build.

I've verified that this patch correctly builds the tracepoint
docbook which currently covers signals, and irqs.

Changes in v2:
 - properly indent perl 'if' statements

Signed-off-by: Jason Baron <jbaron@redhat.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: William Cohen <wcohen@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Masami Hiramatsu <mhiramat@redhat.com>
LKML-Reference: <200912011718.nB1HIn7t011371@int-mx04.intmail.prod.int.phx2.redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>