ARM: dts: Makefile: Add the am335x-evmsk target in dtbs list

The EVMSK was not built with the 'make dtbs' command.
Add the missing entry in the dts Makefile.
Signed-off-by: Benoit Cousson <b-cousson@ti.com>

arch/arm/boot/dts/Makefile

@@ -73,6 +73,7 @@ dtb-$(CONFIG_ARCH_OMAP2PLUS) += omap2420-h4.dtb \
 	omap4-sdp.dtb \
 	omap5-evm.dtb \
 	am335x-evm.dtb \
+	am335x-evmsk.dtb \
 	am335x-bone.dtb
 dtb-$(CONFIG_ARCH_PRIMA2) += prima2-evb.dtb
 dtb-$(CONFIG_ARCH_U8500) += snowball.dtb