Documentation: tracing: Add %return suffix description

Add a description of the %return suffix option for kprobe event and
uprobe event.

Link: https://lkml.kernel.org/r/159972815624.428528.10450874184415697524.stgit@devnote2

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

Documentation/trace/kprobetrace.rst

@@ -30,6 +30,7 @@ Synopsis of kprobe_events
 
   p[:[GRP/]EVENT] [MOD:]SYM[+offs]|MEMADDR [FETCHARGS]	: Set a probe
   r[MAXACTIVE][:[GRP/]EVENT] [MOD:]SYM[+0] [FETCHARGS]	: Set a return probe
+  p:[GRP/]EVENT] [MOD:]SYM[+0]%return [FETCHARGS]	: Set a return probe
   -:[GRP/]EVENT						: Clear a probe
 
  GRP		: Group name. If omitted, use "kprobes" for it.
@@ -37,6 +38,7 @@ Synopsis of kprobe_events
 		  based on SYM+offs or MEMADDR.
  MOD		: Module name which has given SYM.
  SYM[+offs]	: Symbol+offset where the probe is inserted.
+ SYM%return	: Return address of the symbol
  MEMADDR	: Address where the probe is inserted.
  MAXACTIVE	: Maximum number of instances of the specified function that
 		  can be probed simultaneously, or 0 for the default value

Documentation/trace/uprobetracer.rst

@@ -28,6 +28,7 @@ Synopsis of uprobe_tracer
 
   p[:[GRP/]EVENT] PATH:OFFSET [FETCHARGS] : Set a uprobe
   r[:[GRP/]EVENT] PATH:OFFSET [FETCHARGS] : Set a return uprobe (uretprobe)
+  p[:[GRP/]EVENT] PATH:OFFSET%return [FETCHARGS] : Set a return uprobe (uretprobe)
   -:[GRP/]EVENT                           : Clear uprobe or uretprobe event
 
   GRP           : Group name. If omitted, "uprobes" is the default value.
@@ -35,6 +36,7 @@ Synopsis of uprobe_tracer
                   on PATH+OFFSET.
   PATH          : Path to an executable or a library.
   OFFSET        : Offset where the probe is inserted.
+  OFFSET%return : Offset where the return probe is inserted.
 
   FETCHARGS     : Arguments. Each probe can have up to 128 args.
    %REG         : Fetch register REG