coresight-dummy: add dummy driver support for source devices

Add driver support to configure dummy Coresight source
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: I7b68202fc6d7958fcf7ff933d7eed7e19c958ab0
Signed-off-by: Shashank Mittal <mittals@codeaurora.org>
Signed-off-by: Satyajit Desai <sadesai@codeaurora.org>