defconfig: msm8974: Disable appended DT option

Disable the kernel option to append device tree blob
to end of kernel image.  This is no longer necessary
as the Android boot/recovery images will have a
separate section to store the device tree blob.

Change-Id: I6e9ed038d704ffb59a09a58466fc56d68ebe072a
Signed-off-by: David Ng <dave@codeaurora.org>