fw_cfg_build_feature_control() uses CPUID_EXT_VMX which is
defined in "target/i386/cpu.h".

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20230904124325.79040-4-philmd@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>