Add compilation macro for each BL stage

This patch defines a compile time macro for each boot loader stage
which allows compilation of code only for a specific stage.

Change-Id: I3a4068404cd3dc26d652556ca9ca7afea8dd28ef
Reduce the runtime stack size in BL stages.

This patch separates the stack size for each BL stage and
reduces it after stack usage analysis was done.

Fixes ARM-software/tf-issues#200

Change-Id: I8edc6de2551b0a6788761d121937692b2149bb29
Merge pull request #182 from soby-mathew/sm/stack_optimize

Reduce runtime stack size and add compilation macro for each BL stage