OvmfPkg/QemuFwCfgS3Lib: add initial Base Null library instance

This library instance returns constant FALSE from QemuFwCfgS3Enabled(),
and all other library functions trigger assertion failures. It is suitable
for QEMU targets and machine types that never enable S3.

The QemuFwCfgS3Enabled() implementation is copied from
"ArmVirtPkg/Library/QemuFwCfgLib/QemuFwCfgLib.c". Stubs for further
QemuFwCfgS3Lib APIs (with assertion failures, see above) will be added
later.

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>