perf record: Decouple record__mmap_read() and evlist.

perf record: Decouple record__mmap_read() and evlist.

Perf evlist will have multiple mmap arrays. Update record__mmap_read():
it should read from 'struct perf_mmap' directly.

Also, make record__mmap_read() ready to read from backward ring buffer.

Signed-off-by: Wang Nan <[email protected]>
Acked-by: Jiri Olsa <[email protected]>
Cc: He Kuang <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Nilay Vaish <[email protected]>
Cc: Zefan Li <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>