jtagmm: Add debug and etm register save-restore support for krypton

Debug and ETM registers do not retain their state on power collapse.
This change provides save-restore support for these registers using
memory mapped access to allow debugging and tracing across power
collapse.

Change-Id: I5f3b3a9c1deb578b9b4323d8fd18b933077abf79
Signed-off-by: Aparna Das <adas@codeaurora.org>