sysutils/edk2: enable secure boot on bhyve

Everything is ready in edk2 for secure boot. To make use of secure boot
you have to boot into an EFI shell and install your keys. Booting an EFI
shell can be done by starting bhyve without any image attached to it.
More information on how to generate and install keys can be found in the
ACRN documentation [1].

Note that that secure boot capable UEFI implementation is required to
meet the Windows 11 requirements.

[1] https://projectacrn.github.io/3.2/tutorials/waag-secure-boot.html

Reviewed by: manu
Approved by: manu
Sponsored by: Beckhoff Automation GmbH & Co. KG
Differential Revision: https://reviews.freebsd.org/D41869