dts, arm/arm64: Remove dtbs build rules in sub-makes

Add dtb files to build targets and let kbuild handle them. Thus,
special dtbs rules can be removed. This eases Makefiles and the
implementation of the support of vendor dtb subdirectories.

Signed-off-by: Robert Richter <rrichter@cavium.com>

diff --cc arch/arm/Makefile
Simple merge

diff --cc arch/arm/boot/dts/Makefile
Simple merge

diff --cc arch/arm64/Makefile
Simple merge

diff --cc arch/arm64/boot/dts/Makefile
Simple merge