libperf: Adopt simplified perf_evsel__open() function from tools/perf

Add a perf_evsel__open() function to libperf.

It's a simplified version of evsel__open() without the fallback
mechanism.

We can try to merge it in the future to libperf, but it has many
details, lets start simple, requiring the latest kernel, perf should
continue using its evsel__open() version, continuing to support running
on older kernels when possible.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexey Budankov <alexey.budankov@linux.intel.com>
Cc: Andi Kleen <ak@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/20190721112506.12306-63-jolsa@kernel.org


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