[POWERPC] ps3: add a default zImage target

It's currently not possible to build the default zImage
target if PS3 is the only selected platform. This is
a hack to fall back to building the pseries style
zImage, so the build is successful. This will probably
change in the future, if someone writes a PS3 specific
boot wrapper.
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>

arch/powerpc/boot/Makefile

@@ -155,6 +155,7 @@ $(obj)/uImage: vmlinux $(wrapperbits)
 image-$(CONFIG_PPC_PSERIES)		+= zImage.pseries
 image-$(CONFIG_PPC_MAPLE)		+= zImage.pseries
 image-$(CONFIG_PPC_IBM_CELL_BLADE)	+= zImage.pseries
+image-$(CONFIG_PPC_PS3)			+= zImage.pseries
 image-$(CONFIG_PPC_CHRP)		+= zImage.chrp
 image-$(CONFIG_PPC_EFIKA)		+= zImage.chrp
 image-$(CONFIG_PPC_PMAC)		+= zImage.pmac