Separate BL functions out of arch.h

Move the BL function prototypes out of arch.h and into the
appropriate header files to allow more efficient header file
inclusion. Create new BL private header files where there is no
sensible existing header file.

Change-Id: I45f3e10b72b5d835254a6f25a5e47cf4cfb274c3
diff --git a/bl2/bl2_main.c b/bl2/bl2_main.c
index cb0519a..a7159fb 100644
--- a/bl2/bl2_main.c
+++ b/bl2/bl2_main.c
@@ -38,6 +38,7 @@
 #include <bl_common.h>
 #include <bl2.h>
 #include <debug.h>
+#include "bl2_private.h"
 
 /*******************************************************************************
  * The only thing to do in BL2 is to load further images and pass control to