coresight: implement coresight abort

Provide CoreSight abort debug api to stop the active trace sink
from any context. This is a best effort api that can be used to
abruptly stop and disable the current trace sink from anywhere
in the kernel to avoid tracing and hence polluting the trace data
after the point of interest has been executed.

Change-Id: I34c528d9febec4265088a7267dbcf0e7a1f87fcf
Signed-off-by: Pratik Patel <pratikp@codeaurora.org>