tracing: Convert nop macros to static inlines

The ftrace.h file contains several functions as macros when the
functions are disabled due to config options. This patch converts
most of them to static inlines.

There are two exceptions:

  register_ftrace_function() and unregister_ftrace_function()

This is because their parameter "ops" must not be evaluated since
code using the function is allowed to #ifdef out the creation of
the parameter.

This also fixes an error caused by recent changes:

 kernel/trace/trace_irqsoff.c: In function 'start_irqsoff_tracer':
 kernel/trace/trace_irqsoff.c:571: error: expected expression before 'do'

Reported-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>