[POWERPC] Enable make install

make help on powerpc says make install is available.
But it failed due to no rule to make install.

This patch enables make install to work.
Signed-off-by: Akinobu Mita <mita@fixstars.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/Makefile

@@ -166,6 +166,9 @@ define archhelp
   @echo '  *_defconfig     - Select default config from arch/$(ARCH)/configs'
 endef
 
+install:
+	$(Q)$(MAKE) $(build)=$(boot) BOOTIMAGE=$(KBUILD_IMAGE) install
+
 archclean:
 	$(Q)$(MAKE) $(clean)=$(boot)
 

arch/powerpc/boot/Makefile

@@ -176,7 +176,7 @@ $(obj)/zImage:		$(addprefix $(obj)/, $(image-y))
 $(obj)/zImage.initrd:	$(addprefix $(obj)/, $(initrd-y))
 	@rm -f $@; ln $< $@
 
-install: $(CONFIGURE) $(image-y)
+install: $(CONFIGURE) $(addprefix $(obj)/, $(image-y))
 	sh -x $(srctree)/$(src)/install.sh "$(KERNELRELEASE)" vmlinux System.map "$(INSTALL_PATH)" $<
 
 # anything not in $(targets)