ARM: dtb: move all dtb targets to common Makefile

Since the dtb targets have moved to arch/arm/boot/dts/Makefile, sweep
the platforms that have had new targets added recently and move them over.

While I was at it, I also made the dtb generation more generic, i.e. if
the platform is enabled then all dtbs for that platform will be created.

Signed-off-by: Olof Johansson <olof@lixom.net>
Cc: Tony Lindgren <tony@atomide.com>
Cc: David Brown <davidb@codeaurora.com>
Cc: Barry Song <Baohua.Song@csr.com>
Cc: Simon Horman <horms@verge.net.au>
Cc: Rob Herring <rob.herring@calxeda.com>
Cc: Stephen Warren <swarren@wwwdotorg.org>