ArmVirtPkg, OvmfPkg: retire QemuFwCfgS3Enabled() from QemuFwCfgLib

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>