ANDROID: arm64: fix dtb appended target builds

Upstream commit 06995804 ("arm64: Use full path in
KBUILD_IMAGE definition") refactored arm64 build targets and
KBUILD_IMAGE is not a default kernel image target. Hence
android specific -dtb targets are not getting built anymore.

Add CONFIG_BUILD_ARM64_APPENDED_KERNEL_IMAGE_NAME as one of
the default targets to fix that.

Fixes: Change-Id: I1c71b85136f1beeb61782e4646820718c1ccd7e4
       ("ANDROID: ARM64: Allow to choose appended kernel image")
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>