pinctrl: bcm2835: Direct GPIO config changes to generic pinctrl

In order to support GPIO config changes direct these to the generic pinctrl.
This also requires an adjust of the return code for unsupported parameter
otherwise gpiod_configure_flags wont work as expected.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>