ARM: dts: mxs: modify mx23/mx28 dts files to use pinctrl headers

Convert mx23/mx28 dts filed to use the pinctrl header files.

NOTE: During automatic conversion of these files to use the pinconfig
definitions an inconsistency has been found in:
arch/arm/boot/dts/imx28-apx4devkit.dts

According to the comment the function for pad SSP2_SS0 should have
been MX28_PAD_SSP2_SS0__GPIO_2_19, while the given value 0x2131
represents: MX28_PAD_SSP2_SS0__AUART3_TX

I used the later (though probably wrong) definition because that's
what is actually being used in the DTB.

Signed-off-by: Lothar Waßmann <LW@KARO-electronics.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>