OvmfPkg: SmbiosVersionLib: add "plugin" for detecting SMBIOS version

OvmfPkg: SmbiosVersionLib: add "plugin" for detecting SMBIOS version

Introduce a minimal library instance for fetching and validating the
SMBIOS entry point structure exposed by QEMU over fw_cfg. This library is
meant to be hooked into MdeModulePkg/Universal/SmbiosDxe by platform DSC
files, so that the library can set the PCD(s) that SmbiosDxe consumes at
the right moment.

At the moment only SMBIOS 2.x entry points are recognized.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Wei Huang <wei@redhat.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Gabriel L. Somlo <somlo@cmu.edu>
Suggested-by: Jordan Justen <jordan.l.justen@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18174 6f19259b-4bc3-4df7-8a09-765794883524