* dts-mode/dts-mode.el: Add new SMIE-based indentation
Fit within 80 columns.
(dts-re-ident): Use :alpha: and :alnum:.
(dts-mode-syntax-table): Remove redundant entry for &.
Complete entries for < and >. Change entry for _ since only letters
should have word syntax.
(dts-use-smie): New var.
(dts-grammar): New constant.
(dts-indent-rules): New function.
(dts-mode): Remove redundant :syntax-table. Remove :group since that
group doesn't exist anyway.
Set syntax-propertize-function to recognize #include's <...> as a string.
Use dts-grammar depending on dts-use-smie.
(auto-mode-alist): Merge the two entries.