ArmPkg/DefaultExceptionHandlerLib AARCH64: add minimal backtrace to crash dump

ArmPkg/DefaultExceptionHandlerLib AARCH64: add minimal backtrace to crash dump

When dumping the CPU state after an unhandled fault, walk the stack
frames and decode the return addresses so we can show a minimal
backtrace. Unfortunately, we do not have sufficient information to
show the function names, but at least we can see the modules and the
return addresses inside the modules.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Tested-by: Leif Lindholm <leif.lindholm@linaro.org>