tcl: add memory testing functions for board diagnostics

tcl: add memory testing functions for board diagnostics

This is a tcl implementation of public domain tests by Michael Barr,
http://www.barrgroup.com/Embedded-Systems/How-To/Memory-Test-Suite-C

The initial porting is done by Shane Volpe and posted to the mailing
list:
http://www.mail-archive.com/openocd-development@lists.berlios.de/msg16676.html

This patch includes some cosmetic amendments plus hardcodes 32bit word
size (as the code depends on memread32/memwrite32 anyway) which fixes
original code's issue of testing only the first quarter of the
specified nBytes.

Change-Id: I5f3a66f1f16fc4082c7a5a6aba338430646ed21c
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/1455
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-by: Mathias Küster <kesmtp@freenet.de>