tracing: add trace_seq_vprint interface

The code to update the print formats for events requires a vprintf
format in the trace_seq. This patch adds that interface.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/include/linux/trace_seq.h b/include/linux/trace_seq.h
index ba9627f..c68bccb 100644
--- a/include/linux/trace_seq.h
+++ b/include/linux/trace_seq.h
@@ -27,6 +27,8 @@
 #ifdef CONFIG_TRACING
 extern int trace_seq_printf(struct trace_seq *s, const char *fmt, ...)
 	__attribute__ ((format (printf, 2, 3)));
+extern int trace_seq_vprintf(struct trace_seq *s, const char *fmt, va_list args)
+	__attribute__ ((format (printf, 2, 0)));
 extern int
 trace_seq_bprintf(struct trace_seq *s, const char *fmt, const u32 *binary);
 extern void trace_print_seq(struct seq_file *m, struct trace_seq *s);