hwrng: histb - Move driver to drivers/char/hw_random/histb-rng.c

Move to drivers/char/hw_random since histb-(t)rng does not provide
cryptography pseudo rng.

histb-rng is pretty like hisi-rng, but after investigation, we confirm
there is no RNG_PHY_SEED register on histb-rng so a separate driver is
needed.

Still we rename relevant function names to match those in hisi-rng.

Link: https://lore.kernel.org/r/20230401164448.1393336-1-mmyangfl@gmail.com
Signed-off-by: David Yang <mmyangfl@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>