SecurityPkg/DxeImageVerificationLib: Mark the File parameter as OPTIONAL

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2652

According to the File description, the File is optional and can be NULL.

Signed-off-by: Guomin Jiang <guomin.jiang@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Chao Zhang <chao.b.zhang@intel.com>

Reviewed-by: Jian J Wang <jian.j.wang@intel.com>

SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c

@@ -1630,7 +1630,7 @@ EFI_STATUS
 EFIAPI
 DxeImageVerificationHandler (
   IN  UINT32                           AuthenticationStatus,
-  IN  CONST EFI_DEVICE_PATH_PROTOCOL   *File,
+  IN  CONST EFI_DEVICE_PATH_PROTOCOL   *File, OPTIONAL
   IN  VOID                             *FileBuffer,
   IN  UINTN                            FileSize,
   IN  BOOLEAN                          BootPolicy