ARM: mxs: always build ocotp

With this patch ocotp support will always be build into the kernel on mxs.
Otherwise a DT-only kernel fails to link with:

arch/arm/mach-mxs/mach-mxs.c:169: undefined reference to `mxs_get_ocotp'

Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>