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.
This is a snapshot of remoteqdss driver as of msm-4.4 commit
'4c332132fc72dd634004f76d92534995feaad15c'.

Change-Id: I4759e08809c72f1f244ed75643f75b3d97eb5b9b
Signed-off-by: Satyajit Desai <sadesai@codeaurora.org>