SST: Add SST_CREATE_FLASH_LAYOUT flag

This patch renames the SST_RAM_FS flag to SST_CREATE_FLASH_LAYOUT
and clarifies its meaning. This flag indicates that it is required
to create an empty SST flash layout.

The patch also updates the SST integration guide accordingly.

Change-Id: I811aea986db351451042bdc70a47f1736b5b385b
Signed-off-by: Marc Moreno <marc.morenoberengue@arm.com>
diff --git a/CommonConfig.cmake b/CommonConfig.cmake
index 78993f6..954fce8 100755
--- a/CommonConfig.cmake
+++ b/CommonConfig.cmake
@@ -191,8 +191,8 @@
 		set (SST_ENCRYPTION ON)
 	endif()
 
-	if (NOT DEFINED SST_RAM_FS)
-		set (SST_RAM_FS OFF)
+	if (NOT DEFINED SST_CREATE_FLASH_LAYOUT)
+		set (SST_CREATE_FLASH_LAYOUT OFF)
 	endif()
 
 	if (NOT DEFINED SST_VALIDATE_METADATA_FROM_FLASH)