bhyve: add basl support for common table header

Most ACPI tables are using the same header. Make it easy to create this
header by creating a function for it.

Reviewed by: jhb, markj (older version)
Approved by: manu (mentor)
MFC after: 2 weeks
Sponsored by: Beckhoff Automation GmbH & Co. KG
Differential Revision: https://reviews.freebsd.org/D36992