Support for coldplugging more devices

As it turns out, not all buses in Linux will add modalias attributes to their devices in sysfs. One notable exception are MDIO buses. The plugin's scan routine would thus not pick them up.

Fortunately, the information is always available in the device's uevent attribute.

Therefore, default to looking for modaliases in the device's uevent attribute instead, falling back to modalias only if uevent is not availble (this should never happen).