perf tools: Streamline bpf examples and headers installation

perf tools: Streamline bpf examples and headers installation

We were emitting 4 lines, two of them misleading:

  make: Entering directory '/home/acme/git/perf/tools/perf'
  <SNIP>
    INSTALL  lib
    INSTALL  include/bpf
    INSTALL  lib
    INSTALL  examples/bpf
  <SNIP>
  make: Leaving directory '/home/acme/git/perf/tools/perf'

Make it more compact by showing just two lines:

  make: Entering directory '/home/acme/git/perf/tools/perf'
    INSTALL  bpf-headers
    INSTALL  bpf-examples
  make: Leaving directory '/home/acme/git/perf/tools/perf'

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-0nvkyciqdkrgy829lony5925@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>