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/fvp/bl2_fvp_setup.c b/plat/fvp/bl2_fvp_setup.c
index 67f89bc..71bd8c2 100644
--- a/plat/fvp/bl2_fvp_setup.c
+++ b/plat/fvp/bl2_fvp_setup.c
@@ -45,8 +45,10 @@
 extern unsigned long __RO_START__;
 extern unsigned long __RO_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.
@@ -57,6 +59,7 @@
 #define BL2_RO_BASE (unsigned long)(&__RO_START__)
 #define BL2_RO_LIMIT (unsigned long)(&__RO_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
@@ -66,11 +69,11 @@
  */
 #define BL2_COHERENT_RAM_BASE (unsigned long)(&__COHERENT_RAM_START__)
 #define BL2_COHERENT_RAM_LIMIT (unsigned long)(&__COHERENT_RAM_END__)
+#endif
 
 /* Data structure which holds the extents of the trusted SRAM for BL2 */
 static meminfo_t bl2_tzram_layout
-__attribute__ ((aligned(PLATFORM_CACHE_LINE_SIZE),
-		section("tzfw_coherent_mem")));
+__attribute__ ((aligned(PLATFORM_CACHE_LINE_SIZE)));
 
 /* Assert that BL3-1 parameters fit in shared memory */
 CASSERT((PARAMS_BASE + sizeof(bl2_to_bl31_params_mem_t)) <
@@ -209,9 +212,12 @@
 	fvp_configure_mmu_el1(bl2_tzram_layout.total_base,
 			      bl2_tzram_layout.total_size,
 			      BL2_RO_BASE,
-			      BL2_RO_LIMIT,
-			      BL2_COHERENT_RAM_BASE,
-			      BL2_COHERENT_RAM_LIMIT);
+			      BL2_RO_LIMIT
+#if USE_COHERENT_MEM
+			      , BL2_COHERENT_RAM_BASE,
+			      BL2_COHERENT_RAM_LIMIT
+#endif
+			      );
 }
 
 /*******************************************************************************