Make the support for starting in EL2/EL3 customizable. A boot loader or
the Arm Trusted Firmware should start RTEMS in non-secure EL1 mode.
In start.S, use local labels.
For the aarch64/xilinx-zynqmp the support for starting in EL2/EL3 is
disabled by default. For the Qemu xlnx-zcu102 machine, the default is
to start in non-secure EL1 mode. This can be controlled by options, for
example "-machine xlnx-zcu102,secure=on,virtualization=on".
07217e3f5c