The i.MX27 dtb build should be controlled by CONFIG_SOC_IMX27 rather
than CONFIG_SOC_IMX31.
Signed-off-by: NShawn Guo <shawn.guo@linaro.org>
Fixes: cb612390 ("ARM: dts: Only build dtb if associated Arch and/or SoC is enabled")
Cc: <stable@vger.kernel.org>