Implement functions of initialization, finalization and processing of
control command messages coming from control file descriptors.

Allocate control file descriptor as descriptor at struct pollfd object
of evsel_list for atomic poll() operation.
Signed-off-by: Alexey Budankov <alexey.budankov@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/62518ceb-1cc9-2aba-593b-55408d07c1bf@linux.intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>