crypto: powerpc/poly1305 - add depends on BROKEN for now

As discussed in the thread containing
https://lore.kernel.org/linux-crypto/20250510053308.GB505731@sol/

, the
Power10-optimized Poly1305 code is currently not safe to call in softirq
context.  Disable it for now.  It can be re-enabled once it is fixed.

Fixes: ba8f8624 ("crypto: poly1305-p10 - Glue code for optmized Poly1305 implementation for ppc64le")
Cc: stable@vger.kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>