Aya::obj depends on bindgen generated files, and we start
by migrating bindgen generated files.
This commit adds the new aya-obj crate to the workplace
and migrates generated files into the crate. We use core
instead of std in an effort to make the final crate no_std.
Bindgen was run against libbpf v1.0.1.
Refs: #473
Shenghui Ye