arm_cti: add cti command group

arm_cti: add cti command group

Extend the CTI abstraction to be accessible from TCL and
change the 'target' command to accept a cti 'object' instead of a
base address. This also allows accessing CTI instances that are not
related to a configured target.

Change-Id: Iac9ed0edca6f1be00fe93783a35c26077f6bc80a
Signed-off-by: Matthias Welwarsky <matthias.welwarsky@sysgo.com>
Reviewed-on: http://openocd.zylin.com/4031
Tested-by: jenkins
Reviewed-by: Matthias Welwarsky <matthias@welwarsky.de>