bhyve: add helper struct for acpi device handling

To simplify the handling of different acpi devices like qemu fwcfg or a
tpm, add a helper struct. It will handle the reporting of acpi
resources.

Reviewed by: markj
MFC after: 1 week
Sponsored by: Beckhoff Automation GmbH & Co. KG
Differential Revision: https://reviews.freebsd.org/D38327