cbmem_top: Fix comment and remove upper limit

There's no such limit on 64 Bit coreboot builds.

* Fix comment in cbmem.h
* Remove 4 GiB limit on Cavium SoCs

Tested on opencellular/elgon.
Still boots Linux as payload.

Change-Id: I8c9c6a5ff81bee48311e8bf8e383d1a032ea3a6d
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-on: https://review.coreboot.org/c/30609
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
diff --git a/src/include/cbmem.h b/src/include/cbmem.h
index 59f4e10..680284a 100644
--- a/src/include/cbmem.h
+++ b/src/include/cbmem.h
@@ -70,7 +70,8 @@
 
 /* Return the top address for dynamic cbmem. The address returned needs to
  * be consistent across romstage and ramstage, and it is required to be
- * below 4GiB.
+ * below 4GiB for 32bit coreboot builds. On 64bit coreboot builds there's no
+ * upper limit.
  * x86 boards or chipsets must return NULL before the cbmem backing store has
  * been initialized. */
 void *cbmem_top(void);