of: Add stub for of_add_property()

If building with OF Kconfig disabled, this can lead to errors for
drivers utilizing of_add_property().  Add a stub for the add API, as
it exists for the remove variant as well, and to avoid compliation
issues.  Also, export this API so that it can be used by modules.

Signed-off-by: Wesley Cheng <wcheng@codeaurora.org>
Link: https://lore.kernel.org/r/1625908395-5498-5-git-send-email-wcheng@codeaurora.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/of/base.c

@@ -1821,6 +1821,7 @@ int of_add_property(struct device_node *np, struct property *prop)
 
 	return rc;
 }
+EXPORT_SYMBOL_GPL(of_add_property);
 
 int __of_remove_property(struct device_node *np, struct property *prop)
 {

include/linux/of.h

@@ -946,6 +946,11 @@ static inline int of_machine_is_compatible(const char *compat)
 	return 0;
 }
 
+static inline int of_add_property(struct device_node *np, struct property *prop)
+{
+	return 0;
+}
+
 static inline int of_remove_property(struct device_node *np, struct property *prop)
 {
 	return 0;