perf bpf examples: Convert etcsnoop to use bpf_map()

Making the code more compact, end result is the same:

  # trace -e /home/acme/git/perf/tools/perf/examples/bpf/etcsnoop.c
     0.000 (         ): sed/7385 openat(dfd: CWD, filename: "/etc/ld.so.cache", flags: RDONLY|CLOEXEC) ...
  2727.723 (         ): cat/7389 openat(dfd: CWD, filename: "/etc/ld.so.cache", flags: RDONLY|CLOEXEC) ...
  2728.543 (         ): cat/7389 openat(dfd: CWD, filename: "/etc/passwd")                          ...
  ^C

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Luis Cláudio Gonçalves <lclaudio@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-znhgz24p0daux2kay200ovc1@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/examples/bpf/etcsnoop.c

@@ -21,12 +21,8 @@
 
 #include <stdio.h>
 
-struct bpf_map SEC("maps") __augmented_syscalls__ = {
-       .type = BPF_MAP_TYPE_PERF_EVENT_ARRAY,
-       .key_size = sizeof(int),
-       .value_size = sizeof(u32),
-       .max_entries = __NR_CPUS__,
-};
+/* bpf-output associated map */
+bpf_map(__augmented_syscalls__, PERF_EVENT_ARRAY, int, u32, __NR_CPUS__);
 
 struct augmented_filename {
 	int	size;