jtag-mm: enable etm save and restore support for msmzirc

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: I60e2894ddf636a3d1446dfc40403bf0f76deef7a
Signed-off-by: Sarangdhar Joshi <spjoshi@codeaurora.org>