MdePkg/Security2: Mark the File parameter as OPTIONAL.

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



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

Signed-off-by: Guomin Jiang <guomin.jiang@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <liming.gao@intel.com>

Reviewed-by: Liming Gao <liming.gao@intel.com>