crypto: hisilicon - Add debugfs for HPRE

HiSilicon HPRE engine driver uses debugfs to provide debug information,
the usage can be found in /Documentation/ABI/testing/debugfs-hisi-hpre.

Signed-off-by: Zaibo Xu <xuzaibo@huawei.com>
Signed-off-by: Hui Tang <tanghui20@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>