Add image_id to bl1_plat_handle_post/pre_image_load()

This patch adds an argument to bl1_plat_post/pre_image_load() APIs
to make it more future proof. The default implementation of
these are moved to `plat_bl1_common.c` file.

These APIs are now invoked appropriately in the FWU code path prior
to or post image loading by BL1 and are not restricted
to LOAD_IMAGE_V2.

The patch also reorganizes some common platform files. The previous
`plat_bl2_el3_common.c` and `platform_helpers_default.c` files are
merged into a new `plat_bl_common.c` file.

NOTE: The addition of an argument to the above mentioned platform APIs
is not expected to have a great impact because these APIs were only
recently added and are unlikely to be used.

Change-Id: I0519caaee0f774dd33638ff63a2e597ea178c453
Signed-off-by: Soby Mathew <soby.mathew@arm.com>
diff --git a/plat/common/plat_bl_common.c b/plat/common/plat_bl_common.c
new file mode 100644
index 0000000..4123df3
--- /dev/null
+++ b/plat/common/plat_bl_common.c
@@ -0,0 +1,51 @@
+/*
+ * Copyright (c) 2018, ARM Limited and Contributors. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <arch_helpers.h>
+#include <assert.h>
+#include <bl_common.h>
+#include <debug.h>
+#include <errno.h>
+
+/*
+ * The following platform functions are weakly defined. The Platforms
+ * may redefine with strong definition.
+ */
+#pragma weak bl2_el3_plat_prepare_exit
+#pragma weak plat_error_handler
+#pragma weak bl2_plat_preload_setup
+#pragma weak bl2_plat_handle_pre_image_load
+#pragma weak bl2_plat_handle_post_image_load
+#pragma weak plat_try_next_boot_source
+
+void bl2_el3_plat_prepare_exit(void)
+{
+}
+
+void __dead2 plat_error_handler(int err)
+{
+	while (1)
+		wfi();
+}
+
+void bl2_plat_preload_setup(void)
+{
+}
+
+int bl2_plat_handle_pre_image_load(unsigned int image_id)
+{
+	return 0;
+}
+
+int bl2_plat_handle_post_image_load(unsigned int image_id)
+{
+	return 0;
+}
+
+int plat_try_next_boot_source(void)
+{
+	return 0;
+}