defconfig: sm8150: 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: I650dd10a8e2b6546249b0a7bffc2f99101409a22
Signed-off-by: lijuang <lijuang@codeaurora.org>