tracing: Move the trace_seq_* functions into its own trace_seq.c file

The trace_seq_*() functions are a nice utility that allows users to manipulate
buffers with printf() like formats. It has its own trace_seq.h header in
include/linux and should be in its own file. Being tied with trace_output.c
is rather awkward.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

include/linux/trace_seq.h

@@ -25,6 +25,8 @@ trace_seq_init(struct trace_seq *s)
 	s->full = 0;
 }
 
+#define MAX_MEMHEX_BYTES	8
+
 /*
  * Currently only defined when tracing is enabled.
  */