dm: core: support reading a single indexed u32 value

The patch adds helper functions to allow reading a single indexed u32
value from a device-tree property containing multiple u32 values, that
is an array of integers.

Signed-off-by: Dario Binacchi <dariobin@libero.it>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/core/of_access.c b/drivers/core/of_access.c
index 29e705e..8b2ce7a 100644
--- a/drivers/core/of_access.c
+++ b/drivers/core/of_access.c
@@ -485,6 +485,28 @@
 	return 0;
 }
 
+int of_read_u32_index(const struct device_node *np, const char *propname,
+		      int index, u32 *outp)
+{
+	const __be32 *val;
+
+	debug("%s: %s: ", __func__, propname);
+	if (!np)
+		return -EINVAL;
+
+	val = of_find_property_value_of_size(np, propname,
+					     sizeof(*outp) * (index + 1));
+	if (IS_ERR(val)) {
+		debug("(not found)\n");
+		return PTR_ERR(val);
+	}
+
+	*outp = be32_to_cpup(val + index);
+	debug("%#x (%d)\n", *outp, *outp);
+
+	return 0;
+}
+
 int of_read_u64(const struct device_node *np, const char *propname, u64 *outp)
 {
 	const __be64 *val;