perf session: Introduce decompressor in reader object

Introduce a decompressor data structure with pointers to decomp
objects and to zstd object.

We cannot just move session->zstd_data to decomp_data as
session->zstd_data is not only used for decompression.

Adding decompressor data object to reader object and introducing
active_decomp into perf_session object to select current decompressor.

Thus decompression could be executed separately for each data file.

Reviewed-by: Jiri Olsa <jolsa@redhat.com>
Reviewed-by: Riccardo Mancini <rickyman7@gmail.com>
Signed-off-by: Alexey Bayduraev <alexey.v.bayduraev@linux.intel.com>
Tested-by: Riccardo Mancini <rickyman7@gmail.com>
Acked-by: Namhyung Kim <namhyung@gmail.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Antonov <alexander.antonov@linux.intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexei Budankov <abudankov@huawei.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/0eee270cb52aebcbd029c8445d9009fd17709d53.1634113027.git.alexey.v.bayduraev@linux.intel.com


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