ANDROID: ARM64: Allow to choose appended kernel image

By default appended kernel image is Image.gz-dtb.
New config option BUILD_ARM64_APPENDED_KERNEL_IMAGE_NAME
allows to choose between Image.gz-dtb and Image-dtb.

Change-Id: I1c71b85136f1beeb61782e4646820718c1ccd7e4
Signed-off-by: Dmitry Shmidt <dimitrysh@google.com>