pinctrl: madera: Add DT bindings for Cirrus Logic Madera codecs

This is the binding description of the pinctrl driver for Cirrus Logic
Madera codecs. The binding uses the generic pinctrl binding so  the main
purpose here is to describe the device-specific names for groups and
functions.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>