MdeModulePkg/Universal/SmbiosDxe: Scan for existing tables

The default EfiSmbiosProtocol operates on an empty SMBIOS table.
The SMBIOS tables are provided by the bootloader on UefiPayloadPkg.
Scan for existing tables in SmbiosDxe and load them if they seem valid.
This fixes the settings menu not showing any hardware information, instead
only "0 MB RAM" was displayed.
Tests showed that the OS can still see the SMBIOS tables.

SmbiosDxe will get the SMBIOS from a guid Hob.
Also will keep the SmbiosHandle if it is available.

Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Hao A Wu <hao.a.wu@intel.com>
Cc: Dandan Bi <dandan.bi@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Cc: Zhichao Gao <zhichao.gao@intel.com>
Reviewed-by: Hao A Wu <hao.a.wu@intel.com>
Tested-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Signed-off-by: Zhiguang Liu <zhiguang.liu@intel.com>