ASoC: wm8903: Expose GPIOs through gpiolib

Also, update platform_data GPIO handling to have an explicit "don't
touch this pin" option.

Add #defines for the GPIO pin functions.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>