dt-bindings: ingenic,pinctrl: Support pinmux/pinconf nodes

Add YAML to describe the pinmux/pinconf sub-nodes of the pinctrl IP on
Ingenic SoCs.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lore.kernel.org/r/20200720154548.12453-1-paul@crapouillou.net


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>