Altivec is only available for powerpc hosts, so only check for its
availability when the host is powerpc, to avoid error messages being
shown on architectures other than x86, arm or powerpc.
Signed-off-by: WANG Xuerui <git@xen0n.name>
Link: https://lore.kernel.org/r/20230731104911.411964-6-kernel@xen0n.nameSigned-off-by: Song Liu <song@kernel.org>