coresight: prevent multiple map or unmap of same cti trigger channel pair

Do not allow mapping or unmapping the same cti trigin or cti trigout
multiple times onto the same ctm channel. Also prevent reference count
increment or decrement in this case which prevents incorrect enabling
or disabling of cti block.

Change-Id: Iebf7e2799e523f803f4509f5ab75fb238c7097ed
Signed-off-by: Aparna Das <adas@codeaurora.org>