Pull out common code from aarch64 and include

Signed-off-by: Hadi Asyrafi <muhammad.hadi.asyrafi.abdul.halim@intel.com>
Change-Id: I4d0f5e1bb01bcdacbedf8e6c359de594239b645f

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>