tcl/target: start using the new TPIU/SWO support

Create the TPIU and SWO device in target config file.
Replace the target event 'trace-config' with the TPIU/SWO event
'post-enable'.
Extend the existing code in the event handler to properly set the
gpio mode and speed to permit synchronous trace.

This patch is not exhaustive of all the targets that have SWO, but
has to be considered as an initial example.

Change-Id: If4bbf364c0d2aef3ae49951e76507a3b1cfd58e7
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/5859
Tested-by: jenkins
Reviewed-by: Adrian M Negreanu <adrian.negreanu@nxp.com>