hw/boards: Explicit no_sdcard=false as ON_OFF_AUTO_OFF

hw/boards: Explicit no_sdcard=false as ON_OFF_AUTO_OFF

Update MachineClass::no_sdcard default implicit AUTO
initialization to explicit OFF. This flag is consumed
in system/vl.c::qemu_disable_default_devices(). Use
this place to assert we don't have anymore AUTO state.

In hw/ppc/e500.c we add the ppce500_machine_class_init()
method to initialize once all the inherited classes.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20250204200934.65279-3-philmd@linaro.org>