[PATCH] powerpc: Add support for building uImages

powerpc: Add support for building uImages

Add support to build a kernel image bootable by u-boot.
Most of the makefile foo is taken from arch/ppc/boot/images/Makefile

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>