For some reason, only the little-endian flavor of
powerpc provided the zero_bytemask() implementation.
Reported-by: NMichal Sojka <sojkam1@fel.cvut.cz>
Acked-by: NMichael Ellerman <mpe@ellerman.id.au>
Signed-off-by: NChris Metcalf <cmetcalf@ezchip.com>