ST-Link USB support added. Change-Id: I2812646f2895b1529ff3f911edbdce7fa0051c8f Signed-off-by: Mathias K <kesmtp@freenet.de> Reviewed-on: http://openocd.zylin.com/261 Tested-by: jenkins Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>