Bhyve's fwctl only passes the number of vcpus to the guest. That could be done easily by QEMU's fwcfg. Additionally, QEMU's fwcfg has much more features. Bhyve will support all those feature too, when it supports fwcfg.
Add -l bootrom,<path/to/your/UEFI.fd>,fwcfg=qemu to your bhyve cmdline to enable QEMU's fwcfg.
This revision is split into smaller commits at https://github.com/Beckhoff/freebsd-src/commits/phab/corvink/fwcfg