defconfig: kona: Disable BUILD_ARM64_APPENDED_DTB_IMAGE flag

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: I0891552e29d445f0447e7eefde0c008e46f8de03
Signed-off-by: Prakruthi Deepak Heragu <pheragu@codeaurora.org>