crypto: powerpc/poly1305 - Add SIMD fallback

Add a SIMD fallback path for poly1305-p10 by converting the 2^64
based hash state into a 2^44 base.  In order to ensure that the
generic fallback is actually 2^44, add ARCH_SUPPORTS_INT128 to
powerpc and make poly1305-p10 depend on it.

Fixes: ba8f8624 ("crypto: poly1305-p10 - Glue code for optmized Poly1305 implementation for ppc64le")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>