FVP: apply new naming conventions to memory regions

Secure ROM at address 0x0000_0000 is defined as FVP_TRUSTED_ROM
Secure RAM at address 0x0400_0000 is defined as FVP_TRUSTED_SRAM
Secure RAM at address 0x0600_0000 is defined as FVP_TRUSTED_DRAM

BLn_BASE and BLn_LIMIT definitions have been updated and are based on
these new memory regions.

The available memory for each bootloader in the linker script is
defined by BLn_BASE and BLn_LIMIT, instead of the complete memory
region.

TZROM_BASE/SIZE and TZRAM_BASE/SIZE are no longer required as part of
the platform porting.

FVP common definitions are defined in fvp_def.h while platform_def.h
contains exclusively (with a few exceptions) the definitions that are
mandatory in the porting guide. Therefore, platform_def.h now includes
fvp_def.h instead of the other way around.

Porting guide has been updated to reflect these changes.

Change-Id: I39a6088eb611fc4a347db0db4b8f1f0417dbab05
diff --git a/bl31/bl31.ld.S b/bl31/bl31.ld.S
index 34a349f..83ef7e7 100644
--- a/bl31/bl31.ld.S
+++ b/bl31/bl31.ld.S
@@ -36,7 +36,7 @@
 
 
 MEMORY {
-    RAM (rwx): ORIGIN = TZRAM_BASE, LENGTH = TZRAM_SIZE
+    RAM (rwx): ORIGIN = BL31_BASE, LENGTH = BL31_LIMIT
 }