include: coresight: Export coresight_cti_ack_trig API

The coresight_cti_ack_trig API is required by users to
acknowledge a cti interrupt.
Provide it in the header file.

Change-Id: I1cd7ebb41fb7c647b48cddb55cf5a797b09f1a7c
Signed-off-by: Rohit Vaswani <rvaswani@codeaurora.org>