arm: kirkwood: dts: Add openrd-* dtb makefile build targets

The following Kirkwood dtb build targets are currently missing:

kirkwood-openrd-base.dtb
kirkwood-openrd-client.dtb
kirkwood-openrd-ultimate.dtb

This patch adds them to the Makefile to fix the build error.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Chris Packham <judge.packham@gmail.com>
Reviewed-by: Chris Packham <judge.packham@gmail.com>
Signed-off-by: Stefan Roese <sr@denx.de>