[dove] Please change output images from uImages to zImages

[Michael Casadevall]

Can we please switch the dove kernel builds to output normal zImages
in line with all other architectures? We're already going to have to
convert the initramfs to a uInitrd for u-boot, and its easier if we
simply handle all the conversions within flash-kernel, and the CD
builder scripts. In addition, if we ever end up supporting kexec on
dove, having zImage's is probably easier than adding support for
uImages to kexec.
Michael