Merge changes from topic "fw-update-2" into integration

* changes:
  feat(sw_crc32): add software CRC32 support
  refactor(hw_crc32): renamed hw_crc32 to tf_crc32
  feat(fwu): avoid booting with an alternate boot source
  docs(fwu): add firmware update documentation
  feat(fwu): avoid NV counter upgrade in trial run state
  feat(plat/arm): add FWU support in Arm platforms
  feat(fwu): initialize FWU driver in BL2
  feat(fwu): add FWU driver
  feat(fwu): introduce FWU platform-specific functions declarations
  docs(fwu_metadata): add FWU metadata build options
  feat(fwu_metadata): add FWU metadata header and build options