pinctrl: imx: Use struct type for pins

The i.MX pinctrl driver uses 5 different arrays for storing the
informations for pins. This requires five allocations. Instead,
use a struct type which is more cache friendly, readable and
requires less allocations. One array of integers is still needed
since the pinctrl framework forces us to maintain it.
This also adds checks whether the allocations are succesful which
were missing.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>