crypto: hisi-trng - Remove crypto_rng interface

crypto: hisi-trng - Remove crypto_rng interface

drivers/crypto/hisilicon/trng/trng.c exposes the same hardware through
two completely separate interfaces, crypto_rng and hwrng.  However, the
implementation of this is buggy because it permits generation operations
from these interfaces to run concurrently with each other, accessing the
same registers.  That is, hisi_trng_generate() synchronizes with itself
but not with hisi_trng_read().  This results in potential repetition of
output from the RNG, output of non-random values, etc.

Fortunately, there's actually no point in hardware RNG drivers
implementing the crypto_rng interface.  It's not actually used by
anything besides the "rng" algorithm type of AF_ALG, which in turn is
not actually used in practice.  Other crypto_rng hardware drivers are
likewise being phased out, leaving just the hwrng support.

Thus, remove it to simplify the code and avoid conflict (and confusion)
with the hwrng interface which is the one that actually matters.

Fixes: e4d9d10ef4be ("crypto: hisilicon/trng - add support for PRNG")
Cc: stable@vger.kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>