OvmfPkg: introduce QemuFwCfgS3Lib class

This library class will enable driver modules (a) to query whether S3
support was enabled on the QEMU command line, (b) to produce fw_cfg DMA
operations that are to be replayed at S3 resume time.

Declare the library class in OvmfPkg/OvmfPkg.dec, and add the library
class header under OvmfPkg/Include/Library/. At the moment, the only API
we expose is QemuFwCfgS3Enabled(), which we'll first migrate from
QemuFwCfgLib. Further interfaces will be added in later patches.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=394
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>

OvmfPkg/Include/Library/QemuFwCfgS3Lib.h

@@ -0,0 +1,39 @@
+/** @file
+  S3 support for QEMU fw_cfg
+
+  This library class enables driver modules (a) to query whether S3 support was
+  enabled on the QEMU command line, (b) to produce fw_cfg DMA operations that
+  are to be replayed at S3 resume time.
+
+  Copyright (C) 2017, 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.
+**/
+
+#ifndef __FW_CFG_S3_LIB__
+#define __FW_CFG_S3_LIB__
+
+/**
+  Determine if S3 support is explicitly enabled.
+
+  @retval  TRUE   If S3 support is explicitly enabled. Other functions in this
+                  library may be called (subject to their individual
+                  restrictions).
+
+           FALSE  Otherwise. This includes unavailability of the firmware
+                  configuration interface. No other function in this library
+                  must be called.
+**/
+BOOLEAN
+EFIAPI
+QemuFwCfgS3Enabled (
+  VOID
+  );
+
+#endif

OvmfPkg/OvmfPkg.dec

@@ -35,6 +35,10 @@
   #
   QemuFwCfgLib|Include/Library/QemuFwCfgLib.h
 
+  ##  @libraryclass  S3 support for QEMU fw_cfg
+  #
+  QemuFwCfgS3Lib|Include/Library/QemuFwCfgS3Lib.h
+
   ##  @libraryclass  Rewrite the BootOrder NvVar based on QEMU's "bootorder"
   #                  fw_cfg file.
   #