ARM: imx5: generate dtbs for imx5 boards

It helps to generate device tree blobs for imx5 boards with command
'make ARCH=arm dtbs'.
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>

arch/arm/mach-imx/Makefile.boot

@@ -38,5 +38,8 @@ zreladdr-$(CONFIG_SOC_IMX6Q)	+= 0x10008000
 params_phys-$(CONFIG_SOC_IMX6Q)	:= 0x10000100
 initrd_phys-$(CONFIG_SOC_IMX6Q)	:= 0x10800000
 
+dtb-$(CONFIG_MACH_IMX51_DT) += imx51-babbage.dtb
+dtb-$(CONFIG_MACH_IMX53_DT) += imx53-ard.dtb imx53-evk.dtb \
+			       imx53-qsb.dtb imx53-smd.dtb
 dtb-$(CONFIG_SOC_IMX6Q)	+= imx6q-arm2.dtb \
 			   imx6q-sabrelite.dtb