fix(rmmd): add missing padding to RMM Boot Manifest and initialize it

This patch also:
     * Enforces the check of RES0 fields on EL3-RMM boot interface
       and manifest
     * Fixes a couple of nits on the EL3-RMM Boot Interface
       documentation.

Signed-off-by: Javier Almansa Sobrino <javier.almansasobrino@arm.com>
Change-Id: Idb9e38f9fcda2ba0655646a1e2c4fdbabd5cdc40
diff --git a/plat/arm/common/trp/arm_trp_setup.c b/plat/arm/common/trp/arm_trp_setup.c
index 59b4c06..aeacd10 100644
--- a/plat/arm/common/trp/arm_trp_setup.c
+++ b/plat/arm/common/trp/arm_trp_setup.c
@@ -28,6 +28,9 @@
 
 static int arm_trp_process_manifest(rmm_manifest_t *manifest)
 {
+	/* padding field on the manifest must be RES0 */
+	assert(manifest->padding == 0U);
+
 	/* Verify the Boot Manifest Version. Only the Major is considered */
 	if (RMMD_MANIFEST_VERSION_MAJOR !=
 		RMMD_GET_MANIFEST_VERSION_MAJOR(manifest->version)) {