coresight-dummy: add support for dummy sink devices

Add driver support to configure dummy coresight sink
devices. This driver can be used for devices that are
controlled by other subsystems but rely on Linux drivers
to configure rest of the trace path.

Change-Id: I4abd0e2fe54c2258e68bb689a75c06846896a50e
Signed-off-by: Satyajit Desai <sadesai@codeaurora.org>