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/bl32/tsp/aarch64/tsp_entrypoint.S b/bl32/tsp/aarch64/tsp_entrypoint.S
index 1cda165..2714282 100644
--- a/bl32/tsp/aarch64/tsp_entrypoint.S
+++ b/bl32/tsp/aarch64/tsp_entrypoint.S
@@ -108,9 +108,11 @@
 	ldr	x1, =__BSS_SIZE__
 	bl	zeromem16
 
+#if USE_COHERENT_MEM
 	ldr	x0, =__COHERENT_RAM_START__
 	ldr	x1, =__COHERENT_RAM_UNALIGNED_SIZE__
 	bl	zeromem16
+#endif
 
 	/* --------------------------------------------
 	 * Allocate a stack whose memory will be marked
diff --git a/bl32/tsp/tsp.ld.S b/bl32/tsp/tsp.ld.S
index 5d7ffa1..d411ad0 100644
--- a/bl32/tsp/tsp.ld.S
+++ b/bl32/tsp/tsp.ld.S
@@ -98,6 +98,7 @@
         *(xlat_table)
     } >RAM
 
+#if USE_COHERENT_MEM
     /*
      * The base address of the coherent memory section must be page-aligned (4K)
      * to guarantee that the coherent data are stored on their own pages and
@@ -116,12 +117,15 @@
         . = NEXT(4096);
         __COHERENT_RAM_END__ = .;
     } >RAM
+#endif
 
     __BL32_END__ = .;
 
     __BSS_SIZE__ = SIZEOF(.bss);
+#if USE_COHERENT_MEM
     __COHERENT_RAM_UNALIGNED_SIZE__ =
         __COHERENT_RAM_END_UNALIGNED__ - __COHERENT_RAM_START__;
+#endif
 
     ASSERT(. <= BL32_LIMIT, "BL3-2 image has exceeded its limit.")
 }
diff --git a/bl32/tsp/tsp_main.c b/bl32/tsp/tsp_main.c
index 193ba29..2eaca7c 100644
--- a/bl32/tsp/tsp_main.c
+++ b/bl32/tsp/tsp_main.c
@@ -43,7 +43,7 @@
  * of trusted SRAM
  ******************************************************************************/
 extern unsigned long __RO_START__;
-extern unsigned long __COHERENT_RAM_END__;
+extern unsigned long __BL32_END__;
 
 /*******************************************************************************
  * Lock to control access to the console
@@ -63,11 +63,11 @@
 
 /*******************************************************************************
  * The BL32 memory footprint starts with an RO sections and ends
- * with a section for coherent RAM. Use it to find the memory size
+ * with the linker symbol __BL32_END__. Use it to find the memory size
  ******************************************************************************/
 #define BL32_TOTAL_BASE (unsigned long)(&__RO_START__)
 
-#define BL32_TOTAL_LIMIT (unsigned long)(&__COHERENT_RAM_END__)
+#define BL32_TOTAL_LIMIT (unsigned long)(&__BL32_END__)
 
 static tsp_args_t *set_smc_args(uint64_t arg0,
 			     uint64_t arg1,