target/arm: Remove TYPE_AARCH64_CPU

target/arm: Remove TYPE_AARCH64_CPU

The TYPE_AARCH64_CPU class is an abstract type that is the parent of
all the AArch64 CPUs.  It now has no special behaviour of its own, so
we can eliminate it and make the AArch64 CPUs directly inherit from
TYPE_ARM_CPU.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20250429132200.605611-8-peter.maydell@linaro.org