setup: Add helper command to build multiple images
setup: Add helper command to build multiple images

Add helper command for building images for mixed 32bit/64bit
ARM builds. The command allows to specify a secondary MACHINE
and image that will be built next to the primary target.
If no secondary image is specified the rpb-minimal image
will be built.

Change-Id: If7e7d45d66c4f5a76e1d471d4e7b3015821dc1e9
Signed-off-by: Zoltan Kuscsik <557cba61231509d70fbac0f1eb5a4bff058a651e@linaro.org>

96boards/oe-rpb-manifest