The same physical device can export multiple devices. In
this case, the capabilities field now contains a union of
all caps available from all exported V4L2 devices alongside
a V4L2_CAP_DEVICE_CAPS flag that should be used to decide
what capabilities to consider. In our case, we need the
ones from the exported device we are using.
https://bugzilla.gnome.org/show_bug.cgi?id=768195
Add properties to the device with exactly the same keys and sematics
as what pulseaudio uses as property keys.
Also handle the case when a device is probed manually and not through gudev.
https://bugzilla.gnome.org//show_bug.cgi?id=759780
