arm-bsp-extras/scp-firmware: Configure SSU module for SI0

- The SSU module provides API functions to access and configure
  the SSU system control and error detection control registers.
- The SSU test module validates all SSU API functions.
- The test-ssu module is used to test the SSU module using
  the integration test modul

Signed-off-by: Rama Krishna Katta <ramakrishna.katta@arm.com>