Implement "<os firmware='efi'>" support for bhyve driver.
As there are not really lot of options, try to find
"BHYVE_UEFI.fd" firmware which is installed by the
sysutils/uefi-edk2-bhyve FreeBSD port.
If not found, just use the first found firmware
in the firmwares directory (which is configurable via
config file).
Signed-off-by: Roman Bogorodskiy <bogorodskiy@gmail.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
