uboot:disk add get_partition_bynameorindex()

This function will get partition through name or index.This reference
by Digi U-Boot.

disk/part.c

@@ -741,3 +741,33 @@ cleanup:
 	free(dup_str);
 	return ret;
 }
+
+int get_partition_bynameorindex(const char *ifname, const char *dev_str,
+				char *part_nameorindex, disk_partition_t *info)
+{
+	int dev;
+	unsigned long part;
+	block_dev_desc_t *dev_desc;
+
+	dev = get_device(ifname, dev_str, &dev_desc);
+	if (dev < 0)
+		return -1;
+
+	/* Check if partition to update is given as a number */
+	if (!strict_strtoul(part_nameorindex, 16, &part)) {
+		/* Look up partition by number */
+		if (!get_partition_info(dev_desc, part, info))
+			return (int)part;
+		} else {
+			/* Look up partition by name */
+			part = 1;
+			while (!get_partition_info(dev_desc, part, info)) {
+				/* Check if partition name matches */
+				if (!strcmp((char *)info->name, part_nameorindex))
+					return (int)part;
+				part++;
+			}
+		}
+
+	return -1;
+}