ArmVirtPkg, OvmfPkg: retire QemuFwCfgS3Enabled() from QemuFwCfgLib

At this point we're ready to retire QemuFwCfgS3Enabled() from the
QemuFwCfgLib class, together with its implementations in:

- ArmVirtPkg/Library/QemuFwCfgLib/QemuFwCfgLib.c
- OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLib.c

Extend all modules that call the function with a new QemuFwCfgS3Lib class
dependency. Thanks to the previously added library class, instances, and
class resolutions, we can do this switch now as tightly as possible.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=394
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

OvmfPkg/Include/Library/QemuFwCfgLib.h

@@ -179,19 +179,5 @@ QemuFwCfgFindFile (
   OUT  UINTN                 *Size
   );
 
-
-/**
-  Determine if S3 support is explicitly enabled.
-
-  @retval  TRUE   if S3 support is explicitly enabled.
-           FALSE  otherwise. This includes unavailability of the firmware
-                  configuration interface.
-**/
-BOOLEAN
-EFIAPI
-QemuFwCfgS3Enabled (
-  VOID
-  );
-
 #endif