perf augmented_raw_syscalls.bpf: Move 'struct timespec64' to vmlinux.h

If we instead decide to generate vmlinux.h from BTF info, it will be
there:

  $ pahole timespec64
  struct timespec64 {
  	time64_t                   tv_sec;               /*     0     8 */
  	long int                   tv_nsec;              /*     8     8 */

  	/* size: 16, cachelines: 1, members: 2 */
  	/* last cacheline: 16 bytes */
  };

  $

pahole manages to find it from /sys/kernel/btf/vmlinux, that is
generated from the kernel types.

With this linux/bpf.h doesn't need to be included, as its already in the
minimalistic tools/perf/util/bpf_skel/vmlinux/vmlinux.h file or what we
need comes when generating a vmlinux.h file from BTF info, i.e. when
using GEN_VMLINUX_H=1, as noticed by Namyung in a build break before
removing linux/bpf.h.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/Zc_fp6CgDClPhS_O@x1