chore(xilinx): follow kernel doc format for functional documentation

For TF-A, there is no format specified for functional documentation.
For AMD-Xilinx platforms, following kernel-doc format for the functional
documentation to make sure AMD-xilinx documentation is align with
actual code.

For example use kernel-doc from linux to call:
<linux>/scripts/kernel-doc -man -v 1 >/dev/null file...

Signed-off-by: Prasad Kummari <prasad.kummari@amd.com>
Change-Id: Idcc9def408b6c8da35b36f67ef82fc00890e998c
diff --git a/plat/xilinx/versal_net/sip_svc_setup.c b/plat/xilinx/versal_net/sip_svc_setup.c
index f6240f3..0c27dec 100644
--- a/plat/xilinx/versal_net/sip_svc_setup.c
+++ b/plat/xilinx/versal_net/sip_svc_setup.c
@@ -43,6 +43,9 @@
 
 /**
  * sip_svc_setup() - Setup SiP Service
+ *
+ * Return: 0 on success, negative error code on failure.
+ *
  */
 static int32_t sip_svc_setup(void)
 {