Clarify rollback counter updates

Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>

source/chapter3-fwupdate.rst

@@ -118,8 +118,10 @@ Post-capsule install reboot success
 #. If all image tests pass correctly the OS exists the FW update procedure
 #. OS install the image acceptance capsule when all acceptance tests pass
 #. Firmware processes the image acceptance capsule and updates the boot bank
-#. On the next reboot BL2 will detect the new version (rollback counter < fw
-   rollback counter).  It must then update the rollback counters accordingly.
+#. Rollback counter updates
+    * If BL33 can update the rollback counter(s) directly, it should do it on the fly
+    * Otherwise, on the next reboot BL2 must detect the new version 
+      (rollback counter < fw rollback counter)and update the rollback counter(s) accordingly.
 
 Post-capsule install reboot fails before UEFI
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