Currently, the kernel uses CONFIG_DEVICE_TREE to wrap a kernel image
with a fdt blob which means for any given configuration only one dts
file can be selected and so support for only one board can be built

This moves the selection of the default .dts file out of the kernel
config and into the bootwrapper makefile.  The makefile chooses which
images to build based on the kernel config and the dts source file
name is taken directly from the image name.  For example "cuImage.ebony"
will use "ebony.dts" as the device tree source file.

In addition, this patch allows a specific image to be requested from the
command line by adding "cuImage.%" and "treeImage.%" targets to the list
of valid built targets in arch/powerpc/Makefile.  This allows the default
dts selection to be overridden.

Another advantage to this change is it allows a single defconfig to be
supplied for all boards using the same chip family and only differing in
the device tree.

Important note: This patch adds two new zImage targets; zImage.dtb.% and
zImage.dtb.initrd.% for zImages with embedded dtb files.  Currently
there are 5 platforms which require this: ps3, ep405, mpc885ads, ep88xc,
adder875-redboot and ep8248e.  This patch *changes the zImage filenames*
for those platforms.  ie. 'zImage.ps3' is now 'zImage.dtb.ps3'.

This new zImage.dtb targets were added so that the .dts file could be
part of the dependancies list for building them.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Paul Mackerras <paulus@samba.org>