OvmfPkg: install an SSDT with a dynamic OperationRegion called FWDT

"FWDT" ("firmware data") is allocated as EfiReservedMemoryType, with
AllocateReservedPool(). <MdePkg/Include/Library/MemoryAllocationLib.h>
doesn't seem to provide direct access to EfiACPIReclaimMemory, but at this
point the former seems sufficient.

Based on SeaBIOS commit 2062f2ba by Gerd Hoffmann <kraxel@redhat.com>.

v3:
- coding style fixes:
  - BDAT     -> FWDT
  - __packed -> #pragma pack(1)
  - BFLD     -> FIRMWARE_DATA, PCI_WINDOW
  - Bfld     -> FwData
- Ssdt.asl: changed license to 2-clause BSDL, paraphrasing Dsdt.asl

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://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@13573 6f19259b-4bc3-4df7-8a09-765794883524

OvmfPkg/AcpiTables/AcpiTables.inf

@@ -33,6 +33,7 @@
   Facp.aslc
   Facs.aslc
   Dsdt.asl
+  Ssdt.asl
 
 [Packages]
   MdePkg/MdePkg.dec

OvmfPkg/AcpiTables/Ssdt.asl

@@ -0,0 +1,19 @@
+/** @file
+  Placeholder for runtime-generated objects.
+
+  This empty table provides only a header for dynamic copying and extension,
+  and a trigger for QemuInstallAcpiSsdtTable().
+
+  Copyright (C) 2012 Red Hat, Inc.
+
+  This program and the accompanying materials are licensed and made available
+  under the terms and conditions of the BSD License which accompanies this
+  distribution.  The full text of the license may be found at
+  http://opensource.org/licenses/bsd-license.php
+
+  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS, WITHOUT
+  WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
+**/
+
+DefinitionBlock ("Ssdt.aml", "SSDT", 1, "REDHAT", "OVMF    ", 1) {
+}