OvmfPkg/PlatformPei: detect SMRAM at default SMBASE (skeleton)

Introduce the Q35SmramAtDefaultSmbaseInitialization() function for
detecting the "SMRAM at default SMBASE" feature.

For now, the function is only a skeleton, so that we can gradually build
upon the result while the result is hard-coded as FALSE. The actual
detection will occur in a later patch.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1512
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
Message-Id: <20200129214412.2361-6-lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

OvmfPkg/PlatformPei/Platform.c

@@ -792,6 +792,7 @@ InitializePlatform (
   if (FeaturePcdGet (PcdSmmSmramRequire)) {
     Q35BoardVerification ();
     Q35TsegMbytesInitialization ();
+    Q35SmramAtDefaultSmbaseInitialization ();
   }
 
   PublishPeiMemory ();