This system services is based on FreeBSD 12's getentropy(), and is
therefore treated the same way as getentropy() with regards to amount
of entropy bits per data bit.
Reviewed-by: NPaul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/8926)

(cherry picked from commit 8b9896eb293a0861f0b8c191b7a278f176b729e6)