MinPlatformPkg/SecFspWrapperPlatformSecLib: Change TopOfTemporaryRam type

Update the type of TopOfTemporaryRam from UINT32 to UINTN.
This change is intended to support X64 build scenarios.
The original code(line 64) may cast the overflowed result
produced by "(TopOfTemporaryRam - sizeof (UINT32))"from
32bit to 64bit.

Cc: Michael Kubacki <michael.a.kubacki@intel.com>
Cc: Chasel Chiu <chasel.chiu@intel.com>
Cc: Nate DeSimone <nathaniel.l.desimone@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Shenglei Zhang <shenglei.zhang@intel.com>
Reviewed-by: Chasel Chiu <chasel.chiu@intel.com>
Reviewed-by: Michael Kubacki <michael.a.kubacki@intel.com>