libbsd: upgrade to v0.8.2 and expand architecture support

When libbsd still supported uClibc as a C library, we added the architecture
exclusions because uClibc's a.out.h includes linux/a.out.h. The latter only
exists for the specified architectures.

However, glibc doesn't include linux/a.out.h, it instead has its own
implementation and it adds a flag to indicate if a.out is supported on this
architecture or not.

Since libbsd currently only supports glibc-based toolchains, the architecture
exclusions are no longer valid.

On microblaze, the build still fails, but this time because of ELF support.
libbsd explicitly handles architectures and microblaze is not one of them (see
local-elf.h).

Signed-off-by: Carlos Santos <casantos@datacom.ind.br>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>