ARM: dts: add missing imx dtb targets

Add missing imx dtb targets, so that make dtbs can cover all imx dtbs.
It's pretty useful for testing dts changes.
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>

arch/arm/boot/dts/Makefile

@@ -79,7 +79,11 @@ dtb-$(CONFIG_ARCH_MVEBU) += armada-370-db.dtb \
 	armada-370-mirabox.dtb \
 	armada-xp-db.dtb \
 	armada-xp-openblocks-ax3-4.dtb
-dtb-$(CONFIG_ARCH_MXC) += imx27-pdk.dtb \
+dtb-$(CONFIG_ARCH_MXC) += \
+	imx25-karo-tx25.dtb \
+	imx27-apf27.dtb \
+	imx27-pdk.dtb \
+	imx31-bug.dtb \
 	imx51-babbage.dtb \
 	imx53-ard.dtb \
 	imx53-evk.dtb \