Select the GPIO register configuration at runtime rather than through
idefs.

Change-Id: I02ea0a3d61bc81669f32097c32420f0688552231
Signed-off-by: David Brown <davidb@codeaurora.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>