kconfig: handle P_SYMBOL in print_symbol()

Each symbol has a property of type P_SYMBOL since commit
59e89e3ddf85 (kconfig: save location of config symbols).
Handle those properties in print_symbol().

Further, place a pointer to print_symbol() in the comment above the
list of known property type.

Signed-off-by: Dirk Gouders <dirk@gouders.net>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/scripts/kconfig/expr.h b/scripts/kconfig/expr.h
index 94a383b..f63b41b 100644
--- a/scripts/kconfig/expr.h
+++ b/scripts/kconfig/expr.h
@@ -171,6 +171,9 @@ struct symbol {
  * config BAZ
  *         int "BAZ Value"
  *         range 1..255
+ *
+ * Please, also check zconf.y:print_symbol() when modifying the
+ * list of property types!
  */
 enum prop_type {
 	P_UNKNOWN,