tools lib traceevent: Add more debugging to see various internal ring buffer entries

When trace-cmd report --debug is set, show the internal ring buffer
entries like time-extends and padding. This requires adding new kbuffer
API to retrieve these items.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Tzvetomir Stoyanov <tstoyanov@vmware.com>
Link: http://lkml.kernel.org/r/20190401164343.257591565@goodmis.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>