Create BL stage specific translation tables

This patch uses the IMAGE_BL<x> constants to create translation tables specific
to a boot loader stage. This allows each stage to create mappings only for areas
in the memory map that it needs.

Fixes ARM-software/tf-issues#209

Change-Id: Ie4861407ddf9317f0fb890fc7575eaa88d0de51c
Merge pull request #214 from soby-mathew/sm/bl_specific_mmap

Create BL stage specific translation tables