bhyve: add basl support for checksums

The qemu ACPI table loader patches the ACPI tables. After patching them,
checksums aren't correct any more. It has to calculate a new checksum
for the ACPI table. For that reason, basl has to keep track of checksums
and has to cause the qemu loader to create new checksums for the tables.

The qemu ACPI table loader isn't supported yet. However, the address of
all tables is unknown as long as bhyve hasn't finished ACPI table
creation. So, the checksum of tables which include pointer to other
tables are unknown too. This requires tracking of checksums too.

Reviewed by: jhb
Approved by: manu (mentor)
MFC after: 2 weeks
Sponsored by: Beckhoff Automation GmbH & Co. KG
Differential Revision: https://reviews.freebsd.org/D36990

(cherry picked from commit 29578470314c09d4ae3163f151da7d4684fb1428)