xilinx: versal: PLM to ATF handover

Parse the parameter structure the PLM populates, to populate the
bl32 and bl33 image structures.

Signed-off-by: Venkatesh Yadav Abbarapu <venkatesh.abbarapu@xilinx.com>
Change-Id: I317072d1086f6cc6f90883c1b8b6d086ff57b443
diff --git a/docs/plat/xilinx-versal.rst b/docs/plat/xilinx-versal.rst
index 95c89a8..57a363b 100644
--- a/docs/plat/xilinx-versal.rst
+++ b/docs/plat/xilinx-versal.rst
@@ -33,3 +33,11 @@
 
 *   `VERSAL_PLATFORM`: Select the platform. Options:
     -   `versal_virt`	: Versal Virtual platform
+
+# PLM->TF-A Parameter Passing
+------------------------------
+The PLM populates a data structure with image information for the TF-A. The TF-A
+uses that data to hand off to the loaded images. The address of the handoff
+data structure is passed in the ```PMC_GLOBAL_GLOB_GEN_STORAGE4``` register.
+The register is free to be used by other software once the TF-A is bringing up
+further firmware images.