perf namespaces: Add more appropriate set of headers

perf namespaces: Add more appropriate set of headers

We don't need perf.h, that is a kitchen sink, all we need is
perf_events.h for perf_ns_link_info, sys/types.h for pid_t and
linux/types.h for u64, list_head.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Li Zhijian <lizhijian@cn.fujitsu.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-f2uxyaj4s2hmntkrezpa6dqz@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>