bhyve: add basic CRB interface for TPM devices

Add a basic emulation for the command and response buffer interface of
TPM devices. This commit only implements some CRB register and resets
them.

Reviewed by: markj
MFC after: 1 week
Sponsored by: Beckhoff Automation GmbH & Co. KG
Differential Revision: https://reviews.freebsd.org/D40456