pinctrl: imx: don't access the pin function radix tree directly

pinctrl: imx: don't access the pin function radix tree directly

The radix tree containing pin function descriptors should not be
accessed directly by drivers. There are dedicated functions for it. I
suppose this driver does it so that the memory containing the function
description is not duplicated but we're going to address that shortly so
convert it to using generic pinctrl APIs.

Tested-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>