Remove coherent memory from the BL memory maps

This patch extends the build option `USE_COHERENT_MEMORY` to
conditionally remove coherent memory from the memory maps of
all boot loader stages. The patch also adds necessary
documentation for coherent memory removal in firmware-design,
porting and user guides.

Fixes ARM-Software/tf-issues#106

Change-Id: I260e8768c6a5c2efc402f5804a80657d8ce38773
diff --git a/plat/juno/bl31_plat_setup.c b/plat/juno/bl31_plat_setup.c
index c450462..ad8ea43 100644
--- a/plat/juno/bl31_plat_setup.c
+++ b/plat/juno/bl31_plat_setup.c
@@ -48,19 +48,25 @@
  ******************************************************************************/
 extern unsigned long __RO_START__;
 extern unsigned long __RO_END__;
+extern unsigned long __BL31_END__;
 
+#if USE_COHERENT_MEM
 extern unsigned long __COHERENT_RAM_START__;
 extern unsigned long __COHERENT_RAM_END__;
+#endif
 
 /*
- * The next 2 constants identify the extents of the code & RO data region.
- * These addresses are used by the MMU setup code and therefore they must be
- * page-aligned.  It is the responsibility of the linker script to ensure that
- * __RO_START__ and __RO_END__ linker symbols refer to page-aligned addresses.
+ * The next 3 constants identify the extents of the code, RO data region and the
+ * limit of the BL3-1 image.  These addresses are used by the MMU setup code and
+ * therefore they must be page-aligned.  It is the responsibility of the linker
+ * script to ensure that __RO_START__, __RO_END__ & __BL31_END__ linker symbols
+ * refer to page-aligned addresses.
  */
 #define BL31_RO_BASE (unsigned long)(&__RO_START__)
 #define BL31_RO_LIMIT (unsigned long)(&__RO_END__)
+#define BL31_END (unsigned long)(&__BL31_END__)
 
+#if USE_COHERENT_MEM
 /*
  * The next 2 constants identify the extents of the coherent memory region.
  * These addresses are used by the MMU setup code and therefore they must be
@@ -70,6 +76,7 @@
  */
 #define BL31_COHERENT_RAM_BASE (unsigned long)(&__COHERENT_RAM_START__)
 #define BL31_COHERENT_RAM_LIMIT (unsigned long)(&__COHERENT_RAM_END__)
+#endif
 
 /******************************************************************************
  * Placeholder variables for copying the arguments that have been passed to
@@ -178,9 +185,13 @@
 void bl31_plat_arch_setup()
 {
 	configure_mmu_el3(BL31_RO_BASE,
-			  BL31_COHERENT_RAM_LIMIT - BL31_RO_BASE,
+			  (BL31_END - BL31_RO_BASE),
 			  BL31_RO_BASE,
-			  BL31_RO_LIMIT,
+			  BL31_RO_LIMIT
+#if USE_COHERENT_MEM
+			  ,
 			  BL31_COHERENT_RAM_BASE,
-			  BL31_COHERENT_RAM_LIMIT);
+			  BL31_COHERENT_RAM_LIMIT
+#endif
+			  );
 }