arm64/cpu: Mark cpu_die() __noreturn

cpu_die() doesn't return.  Annotate it as such.  By extension this also
makes arch_cpu_idle_dead() noreturn.

Acked-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Link: https://lkml.kernel.org/r/20230216184157.4hup6y6mmspr2kll@treble


Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>