defconfig: msm: Disable BUILD_ARM64_APPENDED_DTB_IMAGE flag for Bengal

Add support to compile the kernel without the dtbs appended to it.
All the dtbs are concatenated to form dtb.img. Boot image with header
version 2 will now have this dtb.img added towards the end at an offset.

Change-Id: I742a5b580e8e964f3f748c119ec4b90f00c2da04
Signed-off-by: Shadab Naseem <snaseem@codeaurora.org>