Fix red in 7e31f2a6d5

While the binary firmware build succeeded, the 'make zip' process failed
because the script that put the default wps image together runs the
device config header through CPP while only looking into the
configuration header directory.

So move the imx233-config.h header out of the target/arm/imx233 and into
export/config where everything is copacetic.

Change-Id: I9914558a892f8ff7ad839818f0a5ef687cc7b997