crypto: testmgr - fix RNG performance in fuzz tests

The performance of the crypto fuzz tests has greatly regressed since
v5.18.  When booting a kernel on an arm64 dev board with all software
crypto algorithms and CONFIG_CRYPTO_MANAGER_EXTRA_TESTS enabled, the
fuzz tests now take about 200 seconds to run, or about 325 seconds with
lockdep enabled, compared to about 5 seconds before.

The root cause is that the random number generation has become much
slower due to commit d4150779 ("random32: use real rng for
non-deterministic randomness").  On my same arm64 dev board, at the time
the fuzz tests are run, get_random_u8() is about 345x slower than
prandom_u32_state(), or about 469x if lockdep is enabled.

Lockdep makes a big difference, but much of the rest comes from the
get_random_*() functions taking a *very* slow path when the CRNG is not
yet initialized.  Since the crypto self-tests run early during boot,
even having a hardware RNG driver enabled (CONFIG_CRYPTO_DEV_QCOM_RNG in
my case) doesn't prevent this.  x86 systems don't have this issue, but
they still see a significant regression if lockdep is enabled.

Converting the "Fully random bytes" case in generate_random_bytes() to
use get_random_bytes() helps significantly, improving the test time to
about 27 seconds.  But that's still over 5x slower than before.

This is all a bit silly, though, since the fuzz tests don't actually
need cryptographically secure random numbers.  So let's just make them
use a non-cryptographically-secure RNG as they did before.  The original
prandom_u32() is gone now, so let's use prandom_u32_state() instead,
with an explicitly managed state, like various other self-tests in the
kernel source tree (rbtree_test.c, test_scanf.c, etc.) already do.  This
also has the benefit that no locking is required anymore, so performance
should be even better than the original version that used prandom_u32().

Fixes: d4150779 ("random32: use real rng for non-deterministic randomness")
Cc: stable@vger.kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>