OvmfPkg: QemuFwCfgLib: extract stateful implementation

The current implementation of QemuFwCfgLib is:
- stateful
- implicitly initialized in the library constructor.

OVMF's SEC runs from read-only memory/flash. When the library is linked
into a SEC binary (which currently never happens), the
"mQemuFwCfgSupported" global variable becomes read-only, making the
library non-functional.

Extract the stateful, implicitly initialized library implementation into a
separate file, making room for a stateless, explicitly queried
implementation that's usable in SEC. Restrict the stateful implementation
to the current, non-SEC clients.

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@15045 6f19259b-4bc3-4df7-8a09-765794883524

OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLib.inf

@@ -1,5 +1,8 @@
 ## @file
 #
+#  Stateful, implicitly initialized fw_cfg library.
+#
+#  Copyright (C) 2013, Red Hat, Inc.
 #  Copyright (c) 2008 - 2012, Intel Corporation. All rights reserved.<BR>
 #
 #  This program and the accompanying materials
@@ -18,7 +21,7 @@
   FILE_GUID                      = fdd53716-31e1-4acc-9007-8bd5d877c96f
   MODULE_TYPE                    = BASE
   VERSION_STRING                 = 1.0
-  LIBRARY_CLASS                  = QemuFwCfgLib
+  LIBRARY_CLASS                  = QemuFwCfgLib|PEIM DXE_DRIVER DXE_RUNTIME_DRIVER DXE_SMM_DRIVER
 
   CONSTRUCTOR                    = QemuFwCfgInitialize
 
@@ -30,6 +33,7 @@
 
 [Sources]
   QemuFwCfgLib.c
+  QemuFwCfgPeiDxe.c
 
 [Sources.IA32]
   Ia32/IoLibExAsm.asm