coresight: add cti enable and disable gate functions

Add support for cti enable and disable functions to allow use
cases that require the ability to control the trigger outputs
independent of the trigger mapping and generation configuration.

Change-Id: Id94809be629bb3939a67e8f6711733810aeb1f37
Signed-off-by: Pratik Patel <pratikp@codeaurora.org>