Set the version and date to fixed fields rather than using
preprocessor macros that don't allow reproducible builds.
As a side-effect, the date string is now spec-compliant.

root@bhyve:~ # dmidecode
# dmidecode 2.12
SMBIOS 2.4 present.
12 structures occupying 514 bytes.
Table at 0x000F101F.

Handle 0x0001, DMI type 0, 24 bytes
BIOS Information
        Vendor: BHYVE
        Version: 1.0
        Release Date: 03/14/2014

Submitted by:	des (original version)
Reviewed by:	tychon
MFC after:	1 week