cpu: Remove capstone meson dependency

Only disas.c requires capstone CFLAGS, not cpu.c.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20221130135241.85060-2-philmd@linaro.org>