feat(xilinx): add SPP/EMU platform support for versal

This patch adds SPP/EMU platform support for Xilinx Versal and
also updating the documentation.

Signed-off-by: Venkatesh Yadav Abbarapu <venkatesh.abbarapu@xilinx.com>
Change-Id: Ibdadec4d00cd33ea32332299e7a00de31dc9d60b
diff --git a/docs/plat/xilinx-versal.rst b/docs/plat/xilinx-versal.rst
index d65b048..91ad6f1 100644
--- a/docs/plat/xilinx-versal.rst
+++ b/docs/plat/xilinx-versal.rst
@@ -43,6 +43,8 @@
 
 *   `VERSAL_PLATFORM`: Select the platform. Options:
     -   `versal_virt`	: Versal Virtual platform
+    -   `spp_itr6`	: SPP ITR6
+    -   `emu_it6`	: EMU ITR6
 
 # PLM->TF-A Parameter Passing
 ------------------------------