tracing: Add TRACE_SYSTEM_VAR to intel-sst

tracing: Add TRACE_SYSTEM_VAR to intel-sst

New code will require TRACE_SYSTEM to be a valid C variable name,
but some tracepoints have TRACE_SYSTEM with '-' and not '_', so
it can not be used. Instead, add a TRACE_SYSTEM_VAR that can
give the tracing infrastructure a unique name for the trace system.

Link: http://lkml.kernel.org/r/20150402142831.GT6023@sirena.org.uk
Acked-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Tested-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>