UefiCpuPkg: Change complex DEBUG_CODE() to DEBUG_CODE_BEGIN/END()

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=3767

Update use of DEBUG_CODE(Expression) if Expression is a complex code
block with if/while/for/case statements that use {}.

Cc: Andrew Fish <afish@apple.com>
Cc: Leif Lindholm <leif@nuviainc.com>
Cc: Michael Kubacki <michael.kubacki@microsoft.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>

UefiCpuPkg/Library/BaseXApicLib/BaseXApicLib.c

@@ -243,7 +243,7 @@ GetApicMode (
   VOID
   )
 {
-  DEBUG_CODE (
+  DEBUG_CODE_BEGIN ();
     {
       MSR_IA32_APIC_BASE_REGISTER  ApicBaseMsr;
 
@@ -259,7 +259,7 @@ GetApicMode (
         ASSERT (ApicBaseMsr.Bits.EXTD == 0);
       }
     }
-  );
+  DEBUG_CODE_END ();
   return LOCAL_APIC_MODE_XAPIC;
 }