mailbox.txt: standardize document format

Each text file under Documentation follows a different
format. Some doesn't even have titles!

Change its representation to follow the adopted standard,
using ReST markups for it to be parseable by Sphinx:

- Add markups for section titles;
- Use :Author: for authorship;
- Mark literal block as such and ident it.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/mailbox.txt

@@ -1,5 +1,8 @@
+============================
 The Common Mailbox Framework
-		Jassi Brar <jaswinder.singh@linaro.org>
+============================
+
+:Author: Jassi Brar <jaswinder.singh@linaro.org>
 
 This document aims to help developers write client and controller
 drivers for the API. But before we start, let us note that the
@@ -13,12 +16,15 @@ similar copies of code written for each platform. Having said that,
 nothing prevents the remote f/w to also be Linux based and use the
 same api there. However none of that helps us locally because we only
 ever deal at client's protocol level.
+
 Some of the choices made during implementation are the result of this
 peculiarity of this "common" framework.
 
 
 
-	Part 1 - Controller Driver (See include/linux/mailbox_controller.h)
+Controller Driver (See include/linux/mailbox_controller.h)
+==========================================================
+
 
 Allocate mbox_controller and the array of mbox_chan.
 Populate mbox_chan_ops, except peek_data() all are mandatory.
@@ -30,12 +36,15 @@ the controller driver should set via 'txdone_irq' or 'txdone_poll'
 or neither.
 
 
-	Part 2 - Client Driver (See include/linux/mailbox_client.h)
+Client Driver (See include/linux/mailbox_client.h)
+==================================================
+
 
 The client might want to operate in blocking mode (synchronously
 send a message through before returning) or non-blocking/async mode (submit
 a message and a callback function to the API and return immediately).
 
+::
 
 	struct demo_client {
 		struct mbox_client cl;