target/arm/machine: remove TARGET_AARCH64 from migration state

target/arm/machine: remove TARGET_AARCH64 from migration state

This exposes two new subsections for arm: vmstate_sve and vmstate_za.
Those sections have a ".needed" callback, which already allow to skip
them when not needed.

vmstate_sve .needed is checking cpu_isar_feature(aa64_sve, cpu).
vmstate_za .needed is checking ZA flag in cpu->env.svcr.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20250512180502.2395029-36-pierrick.bouvier@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>