coresight-etm4x: Controls pertaining to tracer configuration

Tracers can be configured with various options at synthesis
time and knowing what resources are available is important for
SW configuration purposes.

As such adding RO sysfs entries for characteristics related to the
tracer implementation.

Signed-off-by: Pratik Patel <pratikp@codeaurora.org>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>