[SPARC32]: Clean up secondary System.map

From: Stefan Holst <mail@s-holst.de>

The clean target is never called, so instead add this to CLEAN_FILES.

arch/sparc/Makefile

@@ -67,7 +67,8 @@ include/asm-$(ARCH)/asm_offsets.h: arch/$(ARCH)/kernel/asm-offsets.s
 	$(call filechk,gen-asm-offsets)
 
 CLEAN_FILES +=	include/asm-$(ARCH)/asm_offsets.h	\
-		arch/$(ARCH)/kernel/asm-offsets.s
+		arch/$(ARCH)/kernel/asm-offsets.s	\
+		arch/$(ARCH)/boot/System.map
 
 # Don't use tabs in echo arguments.
 define archhelp

arch/sparc/boot/Makefile

@@ -32,6 +32,3 @@ $(obj)/tftpboot.img: $(obj)/piggyback $(obj)/System.map $(obj)/image FORCE
 
 $(obj)/btfix.s: $(obj)/btfixupprep vmlinux FORCE
 	$(call if_changed,btfix)
-
-clean:
-	rm $(obj)/System.map