crypto: hisilicon/trng - add support for PRNG

This patch adds support for pseudo random number generator(PRNG)
in Crypto subsystem.

Signed-off-by: Weili Qian <qianweili@huawei.com>
Reviewed-by: Zaibo Xu <xuzaibo@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>