yocto-bsp: add BBG dtb

As 4.4 is the lowest kernel version in oe-core, we can add the dtb for the
beaglebon green to the list of dtb's to generate.

(From meta-yocto rev: dc77383ca352431cba7cb779899220db4eaa0cba)

Signed-off-by: Anders Darander <anders@chargestorm.se>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta-yocto-bsp/conf/machine/beaglebone.conf

@@ -26,7 +26,7 @@ PREFERRED_PROVIDER_virtual/kernel ?= "linux-yocto"
 PREFERRED_VERSION_linux-yocto ?= "4.12%"
 
 KERNEL_IMAGETYPE = "zImage"
-KERNEL_DEVICETREE = "am335x-bone.dtb am335x-boneblack.dtb"
+KERNEL_DEVICETREE = "am335x-bone.dtb am335x-boneblack.dtb am335x-bonegreen.dtb"
 KERNEL_EXTRA_ARGS += "LOADADDR=${UBOOT_ENTRYPOINT}"
 
 SPL_BINARY = "MLO"