trusty: utils: trusty-ut-ctrl: declare trusty-ut-ctrl.system as cc_test

cc_test is preferred for this test utility for it to
be packaged in the test package instead of impacting
the system_ext partition.

Bug: 367423387
Test: atest TrustyVMUnitTests
Change-Id: If9fb87e33b24be02bbccec47513a295d18fdad72