x86: Add SMBIOS table support

System Management BIOS (SMBIOS) is a specification for how
motherboard and system vendors present management information
about their products in a standard format by extending the BIOS
interface on Intel architecture systems. As of today the latest
spec is 3.0 and can be downloaded from DMTF website. This commit
adds a simple and minimum required implementation.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>