soc: qcom: Add debugfs interface for enabling SOC debug events

Other processors/execution environments may support debug events. Implement
an 'smc instruction' based communications protocol and hook it up to
debugfs.

Change-Id: I3a99dfdac5df7edb874bd449d9abc5a929787758
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>