tracing: rename ftrace_printk() => trace_printk()

Impact: cleanup

Use a more generic name - this also allows the prototype to move
to kernel.h and be generally available to kernel developers who
want to do some quick tracing.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/trace/trace.h

@@ -115,7 +115,7 @@ struct userstack_entry {
 };
 
 /*
- * ftrace_printk entry:
+ * trace_printk entry:
  */
 struct print_entry {
 	struct trace_entry	ent;