Forward-declare AccelState in "qemu/typedefs.h" so structures
using a reference of it (like MachineState in "hw/boards.h")
don't have to include "qemu/accel.h".

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Message-Id: <20221130135641.85328-2-philmd@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>