jtagmm: Add debug and etm register save-restore support for 8909

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: Ibdd8f6f5f6d553b23607a10670c16eebb27f9fc3
Signed-off-by: Xiaogang Cui <xiaogang@codeaurora.org>