tee.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:

- adjust identation of titles;
- mark ascii artwork as a literal block;
- adjust references.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/tee.txt

+=============
 TEE subsystem
+=============
+
 This document describes the TEE subsystem in Linux.
 
 A TEE (Trusted Execution Environment) is a trusted OS running in some
@@ -80,7 +83,7 @@ The GlobalPlatform TEE Client API [5] is implemented on top of the generic
 TEE API.
 
 Picture of the relationship between the different components in the
-OP-TEE architecture.
+OP-TEE architecture::
 
       User space                  Kernel                   Secure world
       ~~~~~~~~~~                  ~~~~~~                   ~~~~~~~~~~~~
@@ -109,10 +112,16 @@ kernel are handled by the kernel driver. Other RPC messages will be forwarded to
 tee-supplicant without further involvement of the driver, except switching
 shared memory buffer representation.
 
-References:
+References
+==========
+
 [1] https://github.com/OP-TEE/optee_os
+
 [2] http://infocenter.arm.com/help/topic/com.arm.doc.den0028a/index.html
+
 [3] drivers/tee/optee/optee_smc.h
+
 [4] drivers/tee/optee/optee_msg.h
+
 [5] http://www.globalplatform.org/specificationsdevice.asp look for
     "TEE Client API Specification v1.0" and click download.