Add __amd64__ to the ifdefs that introduce the "pcicfg" spinlock to witness.
Add __amd64__ to the ifdefs that introduce the "pcicfg" spinlock to
witness.

Approved by:  re (safe amd64 support)

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase