coresight: set invalid default cpu id

Current code sets default CPU id as of CPU0. This causes a failure in
case where device tree declares a CoreSight node that is associated with
a CPU that's not available on that target. This causes complete failure of
the system.

Set default CPU id to -1 to avoid this problem.

Change-Id: I77e5f734666a5f806013d685e89902ce5983cf49
Signed-off-by: Shashank Mittal <mittals@codeaurora.org>