crypto: powerpc/poly1305 - Add poly1305_emit_arch wrapper

Add poly1305_emit_arch with fallback instead of calling assembly
directly.  This is because the state format differs between p10
and that of the generic implementation.

Reported-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Reported-by: Eric Biggers <ebiggers@google.com>
Fixes: 14d31979 ("crypto: powerpc/poly1305 - Add block-only interface")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>