Small cleanups to the cuboot bootwrapper code

[Scott Wood]

David Gibson wrote:
> This patch makes a few small cleanups to the cuboot code.
> 	- It removes the double layered selection of images, via
> cuboot-plat-y, instead having the cuboot platforms directly select a
> suitable image-y (this changes the name of the final cuboot image from
> plain cuImage to cuImage.<platform>).
> 	- Factors out some code in the wrapper that's potentially
> useful to platforms other than uboot.
> 
> Signed-off-by: David Gibson <david at gibson.dropbear.id.au>

Acked-by: Scott Wood <scottwood at freescale.com>

-Scott