When compiling bl31 the el3_exit (lib/el3_runtime/aarch64/context.S) is created using the func macro.
As stated in the header of the func macro it must only be used for functions complying a C-ABI.
Afaik there is no way to specify in the cfi that a function will return to a different ELx ...
Anyway, debug solutions on the market are able to calculate the backtrace down to the lower EL. This is suppressed by creating explicit cfi information RET=X30/LR.
My suggestion is to remove the wrong unwinding information.