x86: support SMBIOS v3

x86: support SMBIOS v3

While presumably of primary use to ARM64 (once the code gets
generalized), we should still support this more modern variant,
allowing for the actual DMI data to reside in memory above 4Gb.

While based on draft version 3.0.0d, it is assumed that the final
version of the specification will not render this implementation
invalid (not the least because Linux 3.19 already makes the same
assumption).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>