dts: pinctrl: Introduce pincfg-node

Many data items that are represented in a pin configuration node are
common and generic.  Pin control bindings should use the properties
defined on a standard way when are applicable; not all of these
properties are relevant or useful for all hardware or binding
structures.  Each individual binding document should state which of
these generic properties, if any, are used, and the structure of the
DT nodes that contain these properties.

This is based on Linux, documentation:
https://www.kernel.org/doc/Documentation/devicetree/bindings/pinctrl/pincfg-node.yaml



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