libperf: Add PERF_RECORD_SAMPLE 'struct sample_event' to perf/event.h

Move the PERF_RECORD_SAMPLE event definition to libperf's event.h header
include.

In order to keep libperf simple, we switch 'u64/u32/u16/u8' types used
events to their generic '__u*' versions.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20190825181752.722-13-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>