crypto: arm[64]/poly1305 - add artifact to .gitignore files

The .S_shipped yields a .S, and the pattern in these directories is to
add that to .gitignore so that git-status doesn't raise a fuss.

Fixes: a6b803b3 ("crypto: arm/poly1305 - incorporate OpenSSL/CRYPTOGAMS NEON implementation")
Fixes: f569ca16 ("crypto: arm64/poly1305 - incorporate OpenSSL/CRYPTOGAMS NEON implementation")
Reported-by: Emil Renner Berthing <kernel@esmil.dk>
Cc: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>