Previous config blocks ATF runtime service communications with SDM mailbox

Signed-off-by: Hadi Asyrafi <muhammad.hadi.asyrafi.abdul.halim@intel.com>
Change-Id: Ia857facd0bd0790056df94ed1e016bcf619a161e

This adds BL31 support to Intel Stratix10 SoCFPGA platform. BL31 in TF-A
supports:
- PSCI calls to enable 4 CPU cores
- PSCI mailbox calls for FPGA reconfiguration

Signed-off-by: Loh Tien Hock <tien.hock.loh@intel.com>