powerpc: sparse: Include headers for __weak symbols

Sometimes when sparse warns about undefined symbols, it isn't
because they should have 'static' added, it's because they're
overriding __weak symbols defined elsewhere, and the header has
been missed.

Fix a few of them by adding appropriate headers.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>