bpftool: Expose attach_type-to-string array to non-cgroup code

Move attach_type_strings into main.h for access in non-cgroup code.
bpf_attach_type is used for non-cgroup attach types quite widely now. So also
complete missing string translations for non-cgroup attach types.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Quentin Monnet <quentin@isovalent.com>
Link: https://lore.kernel.org/bpf/20200429001614.1544-8-andriin@fb.com