kconfig: properly build parser when LKC_GENPARSER=1

The rules didn't actually trigger to rebuild the parser.

Change-Id: Id51aaa9816b069204c119622d60f7b728b762cad
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/10168
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

util/kconfig/Makefile

@@ -327,11 +327,15 @@ $(obj)/zconf.hash.c: $(src)/zconf.gperf
 
 %.tab.c: %.y
 	bison -t -l -b $* -p $(notdir $*) $<
-	cp $@ $@_shipped
+
+%.tab.c_shipped: %.tab.c
+	cp $< $@
 
 %.lex.c: %.l
 	flex -L -P$(notdir $*) -o$@ $<
-	cp $@ $@_shipped
+
+%.lex.c_shipped: %.lex.c
+	cp $< $@
 
 %.hash.c: %.gperf
 	gperf < $< > $@