Check if parse_single_tracepoint_event has already asked for PERF_SAMPLE_TIME.

This is kludgy but short term fix for problems introduced by eac23d1c that
broke 'perf script' by having different sample_types when using multiple
tracepoint events when we use a perf binary that tries to use sample_id_all on
an older kernel.

We need to move counter creation to perf_session, support different
sample_types, etc.

Ongoing work on the perf test infrastructure needs this so that we can create
counters to monitor threads generating specific events, etc.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Tom Zanussi <tzanussi@gmail.com>
Cc: Torok Edwin <edwintorok@gmail.com>
Cc: Ian Munsie <imunsie@au1.ibm.com>
LKML-Reference: <new-submission>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>