pinctrl: fix up device tree bindings

After the Nomadik pin controller was force migrated to generic pin
control bindings, some leftovers in the documentation need to be
cleaned up. The code and device trees are already migrated.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>