Consolidate design and porting documentation

Consolidate firmware-design.md and porting-guide.pm so
that recently added sections fit better with
pre-existing sections. Make the documentation more
consistent in use of terminology.

Change-Id: Id87050b096122fbd845189dc2fe1cd17c3003468
diff --git a/docs/porting-guide.md b/docs/porting-guide.md
index c9e4a50..56467fb 100644
--- a/docs/porting-guide.md
+++ b/docs/porting-guide.md
@@ -616,7 +616,8 @@
 The ARM FVP port also populates the `bl32_meminfo` field in the `bl31_args`
 structure pointed to by `bl2_to_bl31_args` with the extents of memory available
 for use by the BL3-2 image. The memory is allocated in the Secure DRAM from the
-address defined by the constant `BL32_BASE`.
+address defined by the constant `BL32_BASE`. The ARM FVP port currently loads
+the BL3-2 image at the Secure DRAM address `0x6002000`.
 
 The non-secure memory extents used for loading BL3-3 are also initialized in
 this function. This information is accessible in the `bl33_meminfo` field in