target/arm/qmp: Include missing 'cpu.h' header

target/arm/qmp: Include missing 'cpu.h' header

arm-qmp-cmds.c uses ARM_MAX_VQ, which is defined in "cpu.h".
Include the latter to avoid when refactoring unrelated headers:

  target/arm/arm-qmp-cmds.c:83:19: error: use of undeclared identifier 'ARM_MAX_VQ'
     83 | QEMU_BUILD_BUG_ON(ARM_MAX_VQ > 16);
        |                   ^

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Message-id: 20250513173928.77376-8-philmd@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>