pinctrl: imx: move hard-coding data into device tree

Currently, all imx pinctrl drivers maintain a big array of struct
imx_pin_reg which hard-codes data like register offset and mux mode
setting for each pin function.  Every time a new imx SoC support is
added, we need to add such a big mount of data.  With moving to single
kernel build, it's only matter of time to be blamed on memory consuming.

With DTC pre-processor support in place, the patch moves all these data
into device tree by redefining the PIN_FUNC_ID in imxXX-pinfunc.h and
changing the PIN_FUNC_ID parsing code a little bit.

The pin id gets re-numbered based on mux register offset, or config
register offset if the pin has no mux register, so that kernel can
identify the pin id from register offsets provided by device tree.

As a bonus point of the change, those arbitrary magic numbers standing
for particular PIN_FUNC_ID in device tree sources are now replaced by
macros to improve the readability of dts files.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Dong Aisheng <dong.aisheng@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>