perf evlist: Adopt backwards ring buffer state enum

perf evlist: Adopt backwards ring buffer state enum

As this isn't used at all in mmap.h but in evlist.h, so to cut down the
header dependency tree, move it to where it is used.

Also add mmap.h to the places using it but previously getting it
indirectly via evlist.h.

Add missing pthread.h to evlist.h, as it has a pthread_t struct member
and was getting the header via mmap.h.

Noticed while processing a Jiri's libperf batch touching mmap.h, where
almost everything gets rebuilt because evlist.h is so popular, so cut
down't this rebuild the world party.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Song Liu <songliubraving@fb.com>
Link: https://lkml.kernel.org/n/tip-he0uljeftl0xfveh3d6vtode@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>