J-Link serial number config option

Add serial option to jlink config commands, handy when there is more than one
adapter connected.

To select adapter 0123456 for OpenOCD, use

jlink serial 0123456

Change-Id: Ib29ce3f0c4975e1169211721a4531bf4db61f1ee
Signed-off-by: Joerg Fischer <turboj@gmx.de>
Reviewed-on: http://openocd.zylin.com/2521


Tested-by: jenkins
Reviewed-by: Paul Fertser <fercerpav@gmail.com>