docs: coresight: Update documentation for CoreSight to cover CTI

Add new document covering CTI / CTM usage in CoreSight.

Add section in coresight.rst introducing CTI and CTM modules with link
to new document.

Signed-off-by: Mike Leach <mike.leach@linaro.org>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20200320165303.13681-11-mathieu.poirier@linaro.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>