Add perf_evsel__alloc_id()/perf_evsel__free_id() functions to libperf as
internal functions.

Move 'struct perf_sample_id' to internal/evsel.h header and change
'struct perf_sample_id::evsel' to 'struct perf_evsel' and the related
code that touches it.
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 <a.p.zijlstra@chello.nl>
Link: http://lore.kernel.org/lkml/20190913132355.21634-28-jolsa@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>