feat(partition): add interface to init gpt

Current interface 'partition_init' accepts parameter image_id
and returns no value. But the entire partition driver is build
only to parse and handle GPT partitions, so add new interface
gpt_partition_init which would return failure to platform code
if it fails to parse the image.

Change-Id: Iaf574d2ad01a15d0723c1475290c31dc4a078835
Signed-off-by: Govindraj Raja <govindraj.raja@arm.com>
diff --git a/drivers/partition/partition.c b/drivers/partition/partition.c
index eff5c57..c60820d 100644
--- a/drivers/partition/partition.c
+++ b/drivers/partition/partition.c
@@ -460,5 +460,19 @@
  */
 void partition_init(unsigned int image_id)
 {
-	load_partition_table(image_id);
+	int ret;
+
+	ret = load_partition_table(image_id);
+	if (ret != 0) {
+		ERROR("Failed to parse partition with image id = %u\n",
+		      image_id);
+	}
+}
+
+/*
+ * Load a GPT based image.
+ */
+int gpt_partition_init(void)
+{
+	return load_partition_table(GPT_IMAGE_ID);
 }