ppc64: install outside of source tree

Rationale:
	When building outside source tree, install.sh is looked for in the
        obj side.

Status:  tested on ppc64 builds
Signed-off-by: Doug Maxey <dwm@austin.ibm.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

arch/ppc64/boot/Makefile

@@ -118,6 +118,6 @@ $(obj)/imagesize.c: vmlinux.strip
 		>> $(obj)/imagesize.c
 
 install: $(CONFIGURE) $(obj)/$(BOOTIMAGE)
-	sh -x $(src)/install.sh "$(KERNELRELEASE)" "$(obj)/$(BOOTIMAGE)" "$(INSTALL_PATH)"
+	sh -x $(srctree)/$(src)/install.sh "$(KERNELRELEASE)" "$(obj)/$(BOOTIMAGE)" "$(INSTALL_PATH)"
 
 clean-files := $(addprefix $(objtree)/, $(obj-boot) vmlinux.strip)