stdlib: Removed SECURITY from the ArmBoard Script

The ARM Board does not support SECURITY extension at the moment.
This change removes the extension from the config script so that
the board functions properly.

Change-Id: I12a5bdf48803e86739967830204a9eef6057bd36
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/60209
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/python/gem5/components/boards/arm_board.py

@@ -75,6 +75,7 @@ class ArmBoard(ArmSystem, AbstractBoard, KernelDiskWorkload):
     **Limitations**
     * The board currently does not support ruby caches.
     * stage2 walker ports are ignored.
+    * This version does not support SECURITY extension.
     """
     __metaclass__ = ABCMeta