Rework BL2 to BL3-1 hand over interface

This patch reworks BL2 to BL3-1 hand over interface by introducing a
composite structure (bl31_args) that holds the superset of information
that needs to be passed from BL2 to BL3-1.

  - The extents of secure memory available to BL3-1
  - The extents of memory available to BL3-2 (not yet implemented) and
    BL3-3
  - Information to execute BL3-2 (not yet implemented) and BL3-3 images

This patch also introduces a new platform API (bl2_get_bl31_args_ptr)
that needs to be implemented by the platform code to export reference to
bl31_args structure which has been allocated in platform-defined memory.

The platform will initialize the extents of memory available to BL3-3
during early platform setup in bl31_args structure. This obviates the
need for bl2_get_ns_mem_layout platform API.

BL2 calls the bl2_get_bl31_args_ptr function to get a reference to
bl31_args structure. It uses the 'bl33_meminfo' field of this structure
to load the BL3-3 image. It sets the entry point information for the
BL3-3 image in the 'bl33_image_info' field of this structure. The
reference to this structure is passed to the BL3-1 image.

Also fixes issue ARM-software/tf-issues#25

Change-Id: Ic36426196dd5ebf89e60ff42643bed01b3500517
diff --git a/include/bl2.h b/include/bl2.h
index 2955a40..d0ff69b 100644
--- a/include/bl2.h
+++ b/include/bl2.h
@@ -43,6 +43,6 @@
  *****************************************/
 extern void bl2_platform_setup(void);
 extern meminfo *bl2_plat_sec_mem_layout(void);
-extern meminfo *bl2_get_ns_mem_layout(void);
+extern bl31_args *bl2_get_bl31_args_ptr(void);
 
 #endif /* __BL2_H__ */