crypto: powerpc/poly1305 - Add missing poly1305_emit_arch

Rename poly1305_emit_64 to poly1305_emit_arch to conform with
the expectation of the poly1305 library.

Reported-by: Thorsten Leemhuis <linux@leemhuis.info>
Fixes: 14d31979 ("crypto: powerpc/poly1305 - Add block-only interface")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Tested-by: Thorsten Leemhuis <linux@leemhuis.info>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>