include: dt-bindings: Add macros entry point for DTS preprocessor

Introduce <dt-bindings/dt-util.h> file.  It wraps <sys/util_macro.h>
file exposing all macro base definitions to DTS preprocessor.  Once it
contains only prepocessor macros, it can be safely included in DTS,
similar way the <dts/arm/<manufacturer>/pinctrl_<manufacturer>_<soc>.h
files are included.

This provides necessary background to elaborate complex constructions
like variable length macros with zero or more elements.

Signed-off-by: Gerson Fernando Budke <nandojve@gmail.com>