kbuild: clean up *.lex.c and *.tab.[ch] patterns from top-level Makefile

Files suffixed by .lex.c, .tab.[ch] are generated lexers, parsers,
respectively.  Clean them up globally from the top Makefile.

Some of the final host programs those lexer/parser are linked into
are necessary for building external modules, but the intermediates
are unneeded.  They can be cleaned away by 'make clean' instead of
'make mrproper'.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Frank Rowand <frowand.list@gmail.com>

scripts/genksyms/Makefile

@@ -11,5 +11,3 @@ HOSTCFLAGS_lex.lex.o := -I$(src)
 
 # dependencies on generated files need to be listed explicitly
 $(obj)/lex.lex.o: $(obj)/parse.tab.h
-
-clean-files	:= lex.lex.c parse.tab.c parse.tab.h