Add libfido2 to the build

From https://github.com/Yubico/libfido2:

libfido2 provides library functionality and command-line tools to
communicate with a FIDO device over USB, and to verify attestation
and assertion signatures.

libfido2 supports the FIDO U2F (CTAP 1) and FIDO 2.0 (CTAP 2)
protocols.

libfido2 will be used by ssh to support FIDO/U2F keys. It is currently
intended only for use by ssh, and so is installed as a PRIVATELIB and is
placed in the ssh pkgbase package.

This is currently disabled for the 32-bit library build as libfido2 is
not compatible with the COMPAT_32BIT hack in usb_ioctl.h.

Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D32448