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/include/bl31/bl31.h b/include/bl31/bl31.h
index b8c603a..a5539d9 100644
--- a/include/bl31/bl31.h
+++ b/include/bl31/bl31.h
@@ -41,6 +41,7 @@
 /*******************************************************************************
  * Function prototypes
  ******************************************************************************/
+extern void bl31_arch_setup(void);
 extern void bl31_next_el_arch_setup(uint32_t security_state);
 extern void bl31_set_next_image_type(uint32_t type);
 extern uint32_t bl31_get_next_image_type(void);