SST: Update SST flash interface

This patch updates the SST flash interface to:
- add sst_ prefix in SST flash interface
  function
- use tfm_sst_err_t as a return value
- update sst_core to call the new interface
  names
- remove sst_flash_get_phys_address as it
  is not needed

Change-Id: Id0b1659bb33133ad0e5bd9da07aa43da9407ab15
Signed-off-by: Marc Moreno <marc.morenoberengue@arm.com>
3 files changed