coresight: dummy: Add snapshot of Coresight Dummy driver

This is a snapshot of the coresight-dummy driver as of msm-4.9
commit 'f4c5ee9a361ed343cb4ddef14159d4946e3579a3'(coresight: dummy:
Add support for dummy sink devices).

Change-Id: I5f034574205584c6b6c044961bdf60f9348b567e
Signed-off-by: Rama Aparna Mallavarapu <aparnam@codeaurora.org>