ARM: dts: mxs: modify mx23/mx28 dts files to use padconfig defines

Convert mx23/mx28 dts files to use the padconfig defintions from
mxs-pinfunc.h.

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