xtensa: exiting simulator on fatal errors

There was old code to exit the simulator when there is a fatal
error. This updates the #ifdef and the function name so that
it can be used to exit both QEMU and simulator when a fatal
error occurs. This should help with twister runs as this will
fail immediately instead of having wait for timeout.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>