cfg: Added st nucleo board configs.

This patch adds board configs for Nucleo FXXX boards.

Change-Id: I25bfd7d63f734bad710917efa67bc6096aa60ef8
Signed-off-by: Jens Hoffmann <jehoffma@gmail.com>
Reviewed-on: http://openocd.zylin.com/2022
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>