Allow loader.efi to identify non-standard boot setup

PATH_BOOTABLE_TOKEN can be set to a non-standard
path that identifies a device as bootable.

Reviewed by: kevans, bcran
Differential Revision:  https://reviews.freebsd.org/D22062

stand/efi/loader/main.c

@@ -863,6 +863,7 @@ main(int argc, CHAR16 *argv[])
 	archsw.arch_getdev = efi_getdev;
 	archsw.arch_copyin = efi_copyin;
 	archsw.arch_copyout = efi_copyout;
+	archsw.arch_hypervisor = x86_hypervisor;
 	archsw.arch_readin = efi_readin;
 	archsw.arch_zfs_probe = efi_zfs_probe;