perf record: Prepare reading from multiple evlists in record__mmap_read_all()

perf record: Prepare reading from multiple evlists in record__mmap_read_all()

Following commits introduce new evlists to record. This patch adjusts
record__mmap_read_all() and record__mmap_read(): converting original
record__mmap_read_all() to record__mmap_read_evlist(), read from one
evlist; makes record__mmap_read() reading from specific evlist.
record__mmap_read_all() will be improved to read from multiple evlists.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Nilay Vaish <nilayvaish@gmail.com>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1467023052-146749-3-git-send-email-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>