kconfig: split some C files out of zconf.y

I want to compile each C file independently instead of including all
of them from zconf.y.

Split out confdata.c, expr.c, symbol.c, and preprocess.c .
These are low-hanging fruits.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

scripts/kconfig/lkc.h

@@ -108,6 +108,7 @@ const char *str_get(struct gstr *gs);
 /* symbol.c */
 void sym_clear_all_valid(void);
 struct symbol *sym_choice_default(struct symbol *sym);
+struct property *sym_get_range_prop(struct symbol *sym);
 const char *sym_get_string_default(struct symbol *sym);
 struct symbol *sym_check_deps(struct symbol *sym);
 struct property *prop_alloc(enum prop_type type, struct symbol *sym);