crypto.ko: Add hchacha20 from libsodium.

This was added to 'device crypto' in the kernel in
bbb7a2c7c329494e0148026f8568c0da4d8db085 but was missing from the
module.

Reviewed by: markj
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D33522