plat/marvell/armada: allow builds without MSS support

Setting MSS_SUPPORT to 0 also removes requirement for SCP_BL2
definition.
Images build with MSS_SUPPORT=0 will not include service CPUs
FW and will not support PM, FC and other features implemented
in these FW images.

Signed-off-by: Konstantin Porotchkin <kostap@marvell.com>
Change-Id: Idf301ebd218ce65a60f277f3876d0aeb6c72f105
Reviewed-on: https://sj1git1.cavium.com/c/IP/SW/boot/atf/+/37769
Tested-by: sa_ip-sw-jenkins <sa_ip-sw-jenkins@marvell.com>
Reviewed-by: Stefan Chulski <stefanc@marvell.com>
Reviewed-by: Ofer Heifetz <oferh@marvell.com>
Reviewed-by: Nadav Haklai <nadavh@marvell.com>
diff --git a/docs/plat/marvell/armada/build.rst b/docs/plat/marvell/armada/build.rst
index e55ce3c..948e87b 100644
--- a/docs/plat/marvell/armada/build.rst
+++ b/docs/plat/marvell/armada/build.rst
@@ -26,7 +26,7 @@
 
        *u-boot.bin* should be used and not *u-boot-spl.bin*
 
-Set MSS/SCP image path (mandatory only for A7K/8K/CN913x)
+Set MSS/SCP image path (mandatory only for A7K/8K/CN913x when MSS_SUPPORT=1)
 
     .. code:: shell