bpf: Attach raw_tp program with BTF via type name

BTF type id specified at program load time has all
necessary information to attach that program to raw tracepoint.
Use kernel type name to find raw tracepoint.

Add missing CHECK_ATTR() condition.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20191016032505.2089704-8-ast@kernel.org