libfdt now provides methods to iterate through subnodes and properties in a convenient fashion.
Replace our ofw_fdt_{peer,child} searches with calls to their corresponding libfdt methods. Rework ofw_fdt_nextprop to use the fdt_for_each_property_offset macro, making it even more obvious what it's doing.
Side note: I'm not completely sold on how I reworked ofw_fdt_nextprop, but it does read a little easier to me this way. I also think we should probably revise the comment about its return values above since 0 will actually indicate 'no more properties or previous property does not exist' and -1 will indicate 'package does not exist or internal error' -- I consider that out of scope for these changes, though.