perf evsel: Add 'immediate' option

perf evsel: Add 'immediate' option

Add an option to cause a selected event to be enabled immediately when
configured by perf_evsel__config().

This is needed when using the sched_switch tracepoint to follow object
code execution.  By having sched_switch enabled immediately the first
sched_switch event precedes the start of other tracing.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1405332185-4050-34-git-send-email-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>