DeviceTree updates for 4.17: - Sync dtc to upstream version v1.4.6-9-gaadd0b65c987. This adds a bunch more warnings (hidden behind W=1). - Build dtc lexer and parser files instead of using shipped versions. - Rework overlay apply API to take an FDT as input and apply overlays in a single step. - Add a phandle lookup cache. This improves boot time by hundreds of msec on systems with large DT. - Add trivial mcp4017/18/19 potentiometers bindings. - Remove VLA stack usage in DT code.