coresight-tmc: Adding a status interface to sysfs

Knowing the state of various control register is always
useful for degging and tuning.  As such add an entry in
sysfs that expose to userspace the most important registers.

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