microblaze: Makefile clean

Remove unnecessary variables
Signed-off-by: NJason Wu <huanyu@xilinx.com>
Acked-by: NMichal Simek <michal.simek@xilinx.com>

arch/microblaze/Makefile

@@ -69,16 +69,13 @@ export MMU DTB
 
 all: linux.bin
 
-# With make 3.82 we cannot mix normal and wildcard targets
-BOOT_TARGETS1 = linux.bin linux.bin.gz
-BOOT_TARGETS2 = simpleImage.%
-
 archclean:
 	$(Q)$(MAKE) $(clean)=$(boot)
 
-$(BOOT_TARGETS1): vmlinux
+linux.bin linux.bin.gz: vmlinux
 	$(Q)$(MAKE) $(build)=$(boot) $(boot)/$@
-$(BOOT_TARGETS2): vmlinux
+
+simpleImage.%: vmlinux
 	$(Q)$(MAKE) $(build)=$(boot) $(boot)/$@
 
 define archhelp