jtag: drivers: cmsis-dap: add TRST handling

Even when TRST and SRST are not present in reset_config we still should
set them appropriately (to 1) as we can't tristate them anyhow.

Change-Id: Iec5bcf09340136f5e6ccfb05fa2697c53fa6609f
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/3798


Tested-by: jenkins
Reviewed-by: Matthias Welwarsky <matthias@welwarsky.de>
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>