intel: Extend SiP service to support mailbox's RSU

Introduce support for RSU that can be initiated through SMC calls.

Added features as below:
- RSU status
- RSU update
- RSU HPS notify
- RSU get sub-partition

Signed-off-by: Hadi Asyrafi <muhammad.hadi.asyrafi.abdul.halim@intel.com>
Change-Id: I78d5a07688e43da99f03d77dfd45ffb4a78f2e4c
diff --git a/plat/intel/soc/agilex/bl31_plat_setup.c b/plat/intel/soc/agilex/bl31_plat_setup.c
index 13099b4..4b11440 100644
--- a/plat/intel/soc/agilex/bl31_plat_setup.c
+++ b/plat/intel/soc/agilex/bl31_plat_setup.c
@@ -14,6 +14,7 @@
 #include <lib/mmio.h>
 #include <lib/xlat_tables/xlat_tables.h>
 
+#include "socfpga_mailbox.h"
 #include "socfpga_private.h"
 
 static entry_point_info_t bl32_image_ep_info;
@@ -107,6 +108,8 @@
 	/* Signal secondary CPUs to jump to BL31 (BL2 = U-boot SPL) */
 	mmio_write_64(PLAT_CPU_RELEASE_ADDR,
 		(uint64_t)plat_secondary_cpus_bl31_entry);
+
+	mailbox_hps_stage_notify(HPS_EXECUTION_STATE_SSBL);
 }
 
 const mmap_region_t plat_agilex_mmap[] = {