arm64: configs: Remove CONFIG_TRUSTY

* MiCode uses *_user_defconfig which doesn't enable
  CONFIG_TRUSTY. It seems this may be used for some
  controlled environment testing purpose and not
  for production releases.

Change-Id: I107198cb26d616f839fc05ff50d87b12ecbd4404
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>