defconfig: msm: Disable CONFIG_BUILD_ARM64_APPENDED_DTB_IMAGE flag

To support Boot image with header version v2, Disable
CONFIG_BUILD_ARM64_APPENDED_DTB flag in defconfig and
perf_defconfig for sdm670.

Change-Id: I4b0b461bd5321f52c4acc67135f49c78a8250522
Signed-off-by: Rahul Shahare <rshaha@codeaurora.org>