Build smbios.ko as a module for amd64 and i386

For whatever reason, smapi, smbios, vpd are all under the "bios" directory.
smapi is only for i386, so the entire "bios" directory is only built for
i386. Break smapi out, and make only it i386-specific. Then, build the
"bios" directory for both amd64 and i386.

Reviewed by: imp
MFC after: 1 week
Sponsored by: Panasas
Differential Revision: https://reviews.freebsd.org/D8609