MFC r262606, r262607, r262608, r262609, r262610, r269528, r269609, r271133:

 - Move imported dts source from sys/contrib/dts/ to sys/gnu/dts.
 - Fix some missing properties.
 - Import dts-related header files.
 - Update everything to latest vendor branch representing 3.17-rc2
   level of Linux DTS API.
MFC 271140:

  Delete old arm dts tree. This was created by cherry picking from a
  full vendor tree. This worked great until it was time to update, but
  now it is time to update. Hit the rest button by removing this branch
  and re-adding it by a full copy of whatever is in the vendor tree.