microblaze: Fix simpleImage format generation

simpleImage generation was broken for some time. This patch is fixing
steps how simpleImage.*.ub file is generated. Steps are objdump of
vmlinux and create .ub.
Also make sure that there is striped elf version with .strip suffix.
Signed-off-by: Michal Simek <michal.simek@xilinx.com>

arch/microblaze/boot/Makefile

@@ -22,17 +22,19 @@ $(obj)/linux.bin.gz: $(obj)/linux.bin FORCE
 quiet_cmd_cp = CP      $< $@$2
 	cmd_cp = cat $< >$@$2 || (rm -f $@ && echo false)
 
-quiet_cmd_strip = STRIP   $@
+quiet_cmd_strip = STRIP   $< $@$2
 	cmd_strip = $(STRIP) -K microblaze_start -K _end -K __log_buf \
-				-K _fdt_start vmlinux -o $@
+				-K _fdt_start $< -o $@$2
 
 UIMAGE_LOADADDR = $(CONFIG_KERNEL_BASE_ADDR)
+UIMAGE_IN = $@
+UIMAGE_OUT = $@.ub
 
 $(obj)/simpleImage.%: vmlinux FORCE
 	$(call if_changed,cp,.unstrip)
 	$(call if_changed,objcopy)
 	$(call if_changed,uimage)
-	$(call if_changed,strip)
-	@echo 'Kernel: $@ is ready' ' (#'`cat .version`')'
+	$(call if_changed,strip,.strip)
+	@echo 'Kernel: $(UIMAGE_OUT) is ready' ' (#'`cat .version`')'
 
 clean-files += simpleImage.*.unstrip linux.bin.ub