Implemented functions are based on Zstd streaming compression API.

The functions are used in runtime to compress data that come from mmaped
kernel buffer. zstd_init(), zstd_fini() are used for initialization and
finalization to allocate and deallocate internal zstd objects.
zstd_compress_stream_to_records() is used to convert parts of mmaped
kernel buffer into an array of PERF_RECORD_COMPRESSED records.
Signed-off-by: Alexey Budankov <alexey.budankov@linux.intel.com>
Reviewed-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/18bf36f3-b85a-1fe2-dd83-10e0c6069568@linux.intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>