bhyve: allow building device specific ACPI tables

Some ACPI devices require a device specific acpi table. E.g. a TPM2
device requires a TPM2 table. Use the acpi_device_emul struct to define
such a device specific table.

Reviewed by: markj
MFC after: 1 week
Sponsored by: Beckhoff Automation GmbH & Co. KG
Differential Revision: https://reviews.freebsd.org/D39320