Improve BL3-0 documentation

Provide some information about the expected use of BL3-0.

Fixes ARM-software/tf-issues#144

Change-Id: I5c8d59a675578394be89481ae4ec39ca37522750
diff --git a/tools/fip_create/fip_create.c b/tools/fip_create/fip_create.c
index c97204a..d1802b7 100644
--- a/tools/fip_create/fip_create.c
+++ b/tools/fip_create/fip_create.c
@@ -53,7 +53,7 @@
  * const char* format_type_str[] = { "RAW", "ELF", "PIC" };
  */
 
-/* Currently only BL2 and BL31 images are supported. */
+/* The images used depends on the platform. */
 static entry_lookup_list_t toc_entry_lookup_list[] = {
 	{ "Trusted Boot Firmware BL2", UUID_TRUSTED_BOOT_FIRMWARE_BL2,
 	  "bl2", NULL, FLAG_FILENAME },