Add u2f(4), a HID driver for FIDO/U2F security keys

[wulf]

Summary

While FIDO/U2F keys were already supported by the generic uhid(4) and
hidraw(4) drivers, this driver adds some additional features an does
steps to tighten the security of FIDO/U2F access.

• It automatically loads through devd.
• Automatically enables HQ_NO_READAHEAD for FIDO/U2F devices.
• Implements only miminum set of features.
• Do not requires external devfs configuration to set character device permissions.
• Names character device as u2f/# to make possible capsicum or any other pledge()-style sandboxing.

PR: 265528
MFC after: 1 week

[wulf]

Duplicate of D51612