doc: update CMSIS-DAP info to match default driver behaviour

By default the driver will now auto detect attached adapters, it does not
use an internal list any more. Update docs to match this.

Change-Id: I62a9d243cd236a8cf54cbd9d088c4837a8df31bf
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/1902


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