bpf: Merge two CONFIG_BPF entries

'config BPF' exists in both init/Kconfig and kernel/bpf/Kconfig.

Commit b24abcff ("bpf, kconfig: Add consolidated menu entry for bpf
with core options") added the second one to kernel/bpf/Kconfig instead
of moving the existing one.

Merge them together.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/bpf/20240204075634.32969-1-masahiroy@kernel.org