Filter: Add Support For Virtual Ports Modem

Some modem devices like Intel 7560 only offer virtual ports from the vendor driver. In ths case, MM would support create modem with the virtual ports. As the virtual ports do not have parents info, People could use Udev tags ID_MM_VIRTUAL_NAME, ID_MM_VIRTUAL_SUBSYSTEMS and ID_MM_PHYSDEV_UID to set parent info of the virtual ports. Then people could add "virtual" driver and MM_PLUGIN_ALLOWED_VIRTUAL_PHY_UID_TAG in the plugin mm_plugin_create function to match the virtual ports device. The attachment is my local test ModemManger logModemManager.log At the end the fibocom could create modem with the virtual ports.