build(bl31): add symbols for memory layout

Add symbols for mapping the physical memory layout of BL31. There are
symbols that partially satisfy this requirement, however, the naming of
these is inconsistent.

Signed-off-by: Harrison Mutai <harrison.mutai@arm.com>
Change-Id: I413cc4e9d7471582eed61d631bed6214bd17a564
diff --git a/bl31/bl31.ld.S b/bl31/bl31.ld.S
index 5ac83fa..abcae0c 100644
--- a/bl31/bl31.ld.S
+++ b/bl31/bl31.ld.S
@@ -26,6 +26,8 @@
 #endif /* PLAT_EXTRA_LD_SCRIPT */
 
 SECTIONS {
+    RAM_REGION_START = ORIGIN(RAM);
+    RAM_REGION_LENGTH = LENGTH(RAM);
     . = BL31_BASE;
 
     ASSERT(. == ALIGN(PAGE_SIZE),
@@ -198,6 +200,7 @@
 
     ASSERT(. <= BL31_LIMIT, "BL31 image has exceeded its limit.")
 #endif /* SEPARATE_NOBITS_REGION */
+    RAM_REGION_END = .;
 
     /DISCARD/ : {
         *(.dynsym .dynstr .hash .gnu.hash)