kbuild: move flex and bison rules to Makefile.host

Flex and bison are used for kconfig, dtc, genksyms, all of which are
host programs. I never imagine the kernel embeds a parser or a lexer.

Move the flex and bison rules to scripts/Makefile.host. This file is
included only when hostprogs-y etc. is present in the Makefile in the
directory. So, parsing these rules are skipped in most of directories.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

scripts/Makefile.host

 # SPDX-License-Identifier: GPL-2.0
+
+# LEX
+# ---------------------------------------------------------------------------
+quiet_cmd_flex = LEX     $@
+      cmd_flex = $(LEX) -o$@ -L $<
+
+$(obj)/%.lex.c: $(src)/%.l FORCE
+	$(call if_changed,flex)
+
+# YACC
+# ---------------------------------------------------------------------------
+quiet_cmd_bison = YACC    $(basename $@).[ch]
+      cmd_bison = $(YACC) -o $(basename $@).c --defines=$(basename $@).h -t -l $<
+
+$(obj)/%.tab.c $(obj)/%.tab.h: $(src)/%.y FORCE
+	$(call if_changed,bison)
+
 # ==========================================================================
 # Building binaries on the host system
 # Binaries are used during the compilation of the kernel, for example

scripts/Makefile.lib

@@ -187,22 +187,6 @@ $(foreach m, $(notdir $1), \
 	$(addprefix $(obj)/, $(foreach s, $3, $($(m:%$(strip $2)=%$(s)))))))
 endef
 
-# LEX
-# ---------------------------------------------------------------------------
-quiet_cmd_flex = LEX     $@
-      cmd_flex = $(LEX) -o$@ -L $<
-
-$(obj)/%.lex.c: $(src)/%.l FORCE
-	$(call if_changed,flex)
-
-# YACC
-# ---------------------------------------------------------------------------
-quiet_cmd_bison = YACC    $(basename $@).[ch]
-      cmd_bison = $(YACC) -o $(basename $@).c --defines=$(basename $@).h -t -l $<
-
-$(obj)/%.tab.c $(obj)/%.tab.h: $(src)/%.y FORCE
-	$(call if_changed,bison)
-
 # Shipped files
 # ===========================================================================