Tracepoints: add wrapper tracepoint() macro

** Instrumentation API change **

Moving tracepoints from

trace_name(args)
register_trace_name(...)
unregister_trace_name(...)

to

tracepoint(name, args)
register_tracepoint(name, ...)
unregister_tracepoint(name, ...)

This will allow doing macro tricks at the "tracepoint()" macro expansion
site. This will be useful for integration with SystemTAP probes, which
needs to expand an inline assembly with constraints on the arguments.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
CC: Nils Carlson <nils.carlson@ericsson.com>
CC: Steven Rostedt <srostedt@redhat.com>
CC: Josh Stone <jistone@redhat.com>