trace, eMCA: Add a knob to adjust where to save event log

To avoid saving two copies for one H/W event, add a new
file under debugfs to control how to save event log.
Once this file is opened, the perf/trace will be used,
in the meanwhile, kernel will stop printing event log
to the console. On the other hand, if this file is closed,
kernel will print event log to the console again.

Signed-off-by: Chen, Gong <gong.chen@linux.intel.com>
Acked-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Tony Luck <tony.luck@intel.com>