propolis should generate ACPI tables

We're stuck using an old (`edk2-stable202105`) version of OVMF, since it is the last one which featured a compiled-in set of ACPI tables which it presents to the guest OS.  Subsequent versions of OVMF expect the vmm (read: qemu) to generate a set of ACPI tables and expose them via the `fw_cfg` table-loader interface.  We should look to do the same so we can move to a newer bootrom.