jtagv8mm: enable etm save and restore support for 64bit

Some CoreSight ETM registers do not retain their states on power
collapse. Enable save-restore support for these registers using
memory mapped access to allow tracing across power collapse.

Change-Id: Iab070c47954e8a199765e9f11ffaec0afd6da0cd
Signed-off-by: Aparna Das <adas@codeaurora.org>