perf tools: Load eBPF object into kernel

This patch utilizes bpf_object__load() provided by libbpf to load all
objects into kernel.

Committer notes:

Testing it:

When using an incorrect kernel version number, i.e., having this in your
eBPF proggie:

  int _version __attribute__((section("version"), used)) = 0x40100;

For a 4.3.0-rc6+ kernel, say, this happens and needs checking at event
parsing time, to provide a better error report to the user:

  # perf record --event /tmp/foo.o sleep 1
  libbpf: load bpf program failed: Invalid argument
  libbpf: -- BEGIN DUMP LOG ---
  libbpf:

  libbpf: -- END LOG --
  libbpf: failed to load program 'fork=_do_fork'
  libbpf: failed to load object '/tmp/foo.o'
  event syntax error: '/tmp/foo.o'
                       \___ Invalid argument: Are you root and runing a CONFIG_BPF_SYSCALL kernel?

  (add -v to see detail)
  Run 'perf list' for a list of valid events

   Usage: perf record [<options>] [<command>]
      or: perf record [<options>] -- <command> [<options>]

      -e, --event <event>   event selector. use 'perf list' to list available events

If we instead make it match, i.e. use 0x40300 on this v4.3.0-rc6+
kernel, the whole process goes thru:

  # perf record --event /tmp/foo.o -a usleep 1
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.202 MB perf.data ]
  # perf evlist -v
  /tmp/foo.o: type: 1, size: 112, config: 0x9, { sample_period,
  sample_freq }: 4000, sample_type: IP|TID|TIME|CPU|PERIOD, disabled: 1,
  inherit: 1, mmap: 1, comm: 1, freq: 1, task: 1, sample_id_all: 1,
  exclude_guest: 1, mmap2: 1, comm_exec: 1
  #

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: David Ahern <dsahern@gmail.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kaixu Xia <xiakaixu@huawei.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1444826502-49291-6-git-send-email-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

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