clk: add support for clk_is_match()

Add support for clk_is_match() which is required to
know if two clock pointers point to the same exact
physical clock.

Also add a unit test for the new API.

Reviewed-by: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
diff --git a/test/dm/clk.c b/test/dm/clk.c
index f301ecb..676ef21 100644
--- a/test/dm/clk.c
+++ b/test/dm/clk.c
@@ -24,6 +24,7 @@
 	/* Get the same clk port in 2 different ways and compare */
 	ut_assertok(clk_get_by_index(dev, 1, &clk_method1));
 	ut_assertok(clk_get_by_index_nodev(dev_ofnode(dev), 1, &clk_method2));
+	ut_asserteq(clk_is_match(&clk_method1, &clk_method2), true);
 	ut_asserteq(clk_method1.id, clk_method2.id);
 
 	return 0;