intel: Refactor common platform code [3/5]

Pull out mailbox driver into common area as they can be shared between
intel's socfpga platform

Signed-off-by: Hadi Asyrafi <muhammad.hadi.asyrafi.abdul.halim@intel.com>
Change-Id: I4064de1ec668931d77abcb7804f6952b70d33716
diff --git a/plat/intel/soc/stratix10/plat_psci.c b/plat/intel/soc/stratix10/plat_psci.c
index f4a970e..73389c9 100644
--- a/plat/intel/soc/stratix10/plat_psci.c
+++ b/plat/intel/soc/stratix10/plat_psci.c
@@ -16,7 +16,7 @@
 
 #include "platform_def.h"
 #include "s10_reset_manager.h"
-#include "s10_mailbox.h"
+#include "socfpga_mailbox.h"
 
 #define S10_RSTMGR_OFST			0xffd11000
 #define S10_RSTMGR_MPUMODRST_OFST	0x20