Add SWD protocol support to bitbang

Add SWD protocol support to bitbang

This is based on the initial work by Paul Fertser with addition of the
switch sequences and new ACK handling.  In case of WAIT response, the
sticky bits are cleared and the last operation is repeated. The ACK
handling is based on the interpretation of the 8 February 2006 ARM
Debug Interface v5 Architecture Specification

Change-Id: Id50855b1ffff310177ccf9883dc9eb0d1b4458c8
Signed-off-by: Jean-Christian de Rivaz <jc@eclis.ch>
Reviewed-on: http://openocd.zylin.com/2437
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>