dt: add empty of_machine_is_compatible

The patch adds an empty function for non-dt build, so that
drivers migrating to dt can save some '#ifdef CONFIG_OF'.

v3: New patch
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

include/linux/of.h

@@ -326,6 +326,11 @@ static inline int of_alias_get_id(struct device_node *np, const char *stem)
 	return -ENOSYS;
 }
 
+static inline int of_machine_is_compatible(const char *compat)
+{
+	return 0;
+}
+
 #define of_match_ptr(_ptr)	NULL
 #define of_match_node(_matches, _node)	NULL
 #endif /* CONFIG_OF */