microblaze: Fix makefile to work with latest toolchain

When building with latest binutils, vmlinux includes
some sections which need to be stripped out when building
the binary image.
Signed-off-by: Michal Simek <monstr@monstr.eu>

arch/microblaze/boot/Makefile

@@ -8,7 +8,7 @@ obj-y += linked_dtb.o
 
 targets := linux.bin linux.bin.gz simpleImage.%
 
-OBJCOPYFLAGS := -O binary
+OBJCOPYFLAGS := -R .note -R .comment -R .note.gnu.build-id -O binary
 
 # Ensure system.dtb exists
 $(obj)/linked_dtb.o: $(obj)/system.dtb