jtagv8: fix debug and etm registers save and restore path

Locking OS Double Lock during Debug register save sequence can make
the trace unit behave as if it is in no power state. To avoid this
save ETM registers before the trace unit enters this state during
Debug register save sequence and also restore ETM registers only
after OS Double Lock is	unlocked in Debug register restore sequence.

Change-Id: Ic121acef01908406f0ab33b623bac8acd9d2e586
Signed-off-by: Aparna Das <adas@codeaurora.org>