bhyve: add Qemu PPI emulation for TPM devices

Windows requires a physical presence interface to recognize the TPM
device. Qemu's OVMF has an implementation for the PPI which can be
reused. Using the Qemu PPI makes it very easy because we don't have to
implement new PPI functionality into our OVMF. The Qemu implementation
is already there.

Reviewed by: markj
MFC after: 1 week
Sponsored by: Beckhoff Automation GmbH & Co. KG
Differential Revision: https://reviews.freebsd.org/D40462