Revert "perf: Disable PERF_RECORD_MMAP2 support"

Revert "perf: Disable PERF_RECORD_MMAP2 support"

This reverts commit 3cc65ba686b5ddabb52950f831ce75c421e33a9a.

Re-enable the mmap2 interface as we will have a user soon.

Since things have changed since perf disabled mmap2, small tweaks
to the revert had to be done:

o commit 8f99de52 forced (n!=8) to become (n<7)
o a new libunwind test needed updating to use mmap2 interface

Signed-off-by: Don Zickus <dzickus@redhat.com>
Link: http://lkml.kernel.org/r/1401461382-209586-1-git-send-email-dzickus@redhat.com
Signed-off-by: Jiri Olsa <jolsa@kernel.org>