s390/boot: pad bzImage to 4K

In order to be able to sign the bzImage independent of the block size
of the IPL device, align the bzImage to 4096 bytes.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/boot/Makefile

@@ -50,6 +50,7 @@ define cmd_section_cmp
 	touch $@
 endef
 
+OBJCOPYFLAGS_bzImage := --pad-to $$(readelf -s $(obj)/compressed/vmlinux | awk '/\<_end\>/ {print or(strtonum("0x"$$2),4095)+1}')
 $(obj)/bzImage: $(obj)/compressed/vmlinux $(obj)/section_cmp.boot.data $(obj)/section_cmp.boot.preserved.data FORCE
 	$(call if_changed,objcopy)