coresight: etm4x: Configure tracers to emit timestamps

Configure timestamps to be emitted at regular intervals in the trace
stream to temporally correlate instructions executed on different CPUs.

Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Tested-by: Leo Yan <leo.yan@linaro.org>
Tested-by: Robert Walker <robert.walker@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>