coresight-etm4x: Controls pertaining to the sequencer functions

Adding sysfs entries to access the sequencers related registers,
more specifically the sequencer state, the sequencer state
transition and the sequencer reset control registers.

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>