OvmfPkg/SMBIOS: Add QEMU support to OVMF SMBIOS driver

OvmfPkg/SMBIOS: Add QEMU support to OVMF SMBIOS driver

Locate QEMU SMBIOS data in fw_cfg and install it via the
SMBIOS protocol.

Starting with qemu-2.1, on pc/x86 machines of type >= 2.1, full
SMBIOS tables are generated and inserted into fw_cfg (i.e., no
per-field patching of locally generated structures is required).

Aside from new code to extract a SMBIOS blob from fw_cfg, this
patch utilizes the pre-existing infrastructure (already used by
Xen) to handle final SMBIOS table creation.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Gabriel Somlo <somlo@cmu.edu>
Reviewed-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@15542 6f19259b-4bc3-4df7-8a09-765794883524