drm/modesetting: add initial gettable properites code.

This allow the user to retrieve a list of properties for an output.
Properties can either be 32-bit values or an enum with an associated name.
Range properties are to be supported.

This API is probably not all correct, I may make properties part of the general
resource get when I think about it some more.

So basically you can create properties and attached them to whatever outputs you want,
so it should be possible to create some generics and just attach them to every output.