This patch adds capability to load BL images based on image
descriptors instead of hard coded way of loading BL images.
This framework is designed such that it can be readily adapted
by any BL stage that needs to load images.

In order to provide the above capability the following new
platform functions are introduced:

  bl_load_info_t *plat_get_bl_image_load_info(void);
    This function returns pointer to the list of images that the
    platform has populated to load.

  bl_params_t *plat_get_next_bl_params(void);
    This function returns a pointer to the shared memory that the
    platform has kept aside to pass trusted firmware related
    information that next BL image needs.

  void plat_flush_next_bl_params(void);
    This function flushes to main memory all the params that
    are passed to next image.

  int bl2_plat_handle_post_image_load(unsigned int image_id)
    This function can be used by the platforms to update/use
    image information for given `image_...