IntelFsp2Pkg: Update SEC_IDT_TABLE struct

REF:https://bugzilla.tianocore.org/show_bug.cgi?id=3957
The reserved IDT table size in SecCore is too small for X64. Changed the type
of IdtTable in SEC_IDT_TABLE from UINT64 to IA32_IDT_GATE_DESCRIPTOR to have
sufficient size reserved in IdtTable for X64.

Cc: Chasel Chiu <chasel.chiu@intel.com>
Cc: Nate DeSimone <nathaniel.l.desimone@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Cc: Ashraf Ali S <ashraf.ali.s@intel.com>
Signed-off-by: Ted Kuo <ted.kuo@intel.com>
Reviewed-by: Chasel Chiu <chasel.chiu@intel.com>

IntelFsp2Pkg/FspSecCore/SecFsp.h

@@ -30,7 +30,7 @@
   @return                     FSP specific IDT gate descriptor.
 
 **/
-UINT64
+IA32_IDT_GATE_DESCRIPTOR
 FspGetExceptionHandler (
   IN  UINT64  IdtEntryTemplate
   );