GitLab

This patch adds a brief explanation of the top/bottom load approach
to the Firmware Design guide and how Trusted Firmware keeps track of
the free memory at boot time. This will help platform developers to
avoid unexpected results in the memory layout.

Fixes ARM-software/tf-issues#319

Change-Id: I04be7e24c1f3b54d28cac29701c24bf51a5c00ad