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/Makefile b/Makefile
index 83b8808..06422ea 100644
--- a/Makefile
+++ b/Makefile
@@ -192,8 +192,8 @@
 				common/${ARCH}/debug.S			\
 				lib/${ARCH}/cache_helpers.S		\
 				lib/${ARCH}/misc_helpers.S		\
+				plat/common/plat_bl_common.c		\
 				plat/common/plat_log_common.c		\
-				plat/common/platform_helpers_default.c	\
 				plat/common/${ARCH}/plat_common.c	\
 				plat/common/${ARCH}/platform_helpers.S	\
 				${COMPILER_RT_SRCS}			\