dt-bindings: pinctrl: Convert generic pin mux and config properties to schema

dt-bindings: pinctrl: Convert generic pin mux and config properties to schema

As pinctrl bindings have a flexible structure and no standard child node
naming convention, creating a single pinctrl schema doesn't work. Instead,
create schemas for the pin mux and config nodes which device pinctrl schema
can reference.

Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: linux-gpio@vger.kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20191107224254.15712-1-robh@kernel.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>