platform/x86: dcdbas: Check SMBIOS for protected buffer address

Add support for a new method for BIOS to provide the address and length
of the protected SMI communication buffer, via SMBIOS OEM strings.

Signed-off-by: Stuart Hayes <stuart.w.hayes@gmail.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>