tcl/interface/ftdi: add Digilent JTAG-SMT2 config

Tested on ZedBoard by Tim Sander.

Change-Id: I4316d9b4d36f01bbe91a46c78ea8bca22efb1a5a
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/2029


Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>