test(ff-a): ffa_spm_id_get

Added few comments related to FF-A v1.1 SPM_ID_GET implementation,
a vmapi helper and two Hafnium CI tests.

Change-Id: I6041bf2ae38abe3b27768b0638164284226137f1
Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
diff --git a/src/api.c b/src/api.c
index a664811..fd2e33f 100644
--- a/src/api.c
+++ b/src/api.c
@@ -464,7 +464,9 @@
 }
 
 /**
- * Returns the ID of the SPMC.
+ * Returns the SPMC FF-A ID at NS virtual/physical and secure virtual
+ * FF-A instances.
+ * DEN0077A FF-A v1.1 Beta0 section 13.9 FFA_SPM_ID_GET.
  */
 struct ffa_value api_ffa_spm_id_get(void)
 {