ARM: build correct dtbs to append to zImage

The boot/dts/Makefile and boot/dts/*/Makefile provide DTB_LIST which is
equal to dtb-y when CONFIG_BUILD_ARM_APPENDED_DTB_IMAGE=y.
Include these Makefiles to build dtbs for dtb appended zImage.

Change-Id: Ib8218135dc923d1ba4098d74dbd7da159368a188
Signed-off-by: Joonwoo Park <joonwoop@codeaurora.org>
[abhimany: resolve trivial merge conflict]
Signed-off-by: Abhimanyu Kapur <abhimany@codeaurora.org>
[sramana: Fixed merge conflicts]
Signed-off-by: Srinivas Ramana <sramana@codeaurora.org>
[jshriram: Fix trivial merge conflicts]
Signed-off-by: Jeevan Shriram <jshriram@codeaurora.org>
[akdwived: Fix trivial merge conflicts]
Signed-off-by: Avaneesh Kumar Dwivedi <akdwived@codeaurora.org>