libs/bsd: implemented dl_iterate_phdr

dl_iterate_phdr now fills the first four fields of
struct dl_phdr_info. The last four fields remain
unimplemented, as it requires help from the
runtime_loader.

Change-Id: Id96a7c7ac05633a71b9fb62c98b3a40f7d4f255b
Signed-off-by: Augustin Cavalier <waddlesplash@gmail.com>