ddcutildisplay: give some time before changing brightness after the monitor resumes

It seems after monitor resume we need to get some time to get monitor initialized, otherwise I get sometimes this:

org.kde.powerdevil: [DDCutilDisplay]: ddca_open_display2 -3029

Still testing.

Also, marking the monitor as unsupported for brightness control after the first unsuccessful attempt is faulty because DDC can be unstable. We probably need to mark it as unsupported after several attempts

void DDCutilDisplay::ddcBrightnessChangeFinished(bool isSuccessful)
{
    if (!isSuccessful) {
        m_supportsBrightness = false;
        Q_EMIT supportsBrightnessChanged(false);
    }
}