Acknowledge that FWU tests do not work on AEM FVP revC

Mention this as a known issue in the change log.

Also update the run_fwu_fvp.sh script to invoke the revB version
of the FVP rather than the revC.

Change-Id: I58957f4ac3ee37e054fe33bfb246c6f6fc689fdd
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>
diff --git a/docs/change-log.rst b/docs/change-log.rst
index 912a35a..190b582 100644
--- a/docs/change-log.rst
+++ b/docs/change-log.rst
@@ -191,6 +191,9 @@
 FWU images
 ``````````
 
+-  The FWU tests do not work on the revC of the Base AEM FVP. They only work on
+   the revB.
+
 -  NS-BL1U and NS-BL2U images reuse TFTF-specific code for legacy reasons. This
    is not a clean design and may cause confusion.