This commit reworks the file generation for Nios II enabling correct
hosted boot by C5 SoC ARM.
- Add bitstream update capability in Quartus makefile. This bypasses a
  complete recompilation of the bitstream.
- Add Nios II makefile targets to generate the needed boot files (if
  hosted boot is enabled in board.settings)
- Enable tightly-coupled memory initialisation by FPGA bitstream
  configuration
- Update documentation for C5 SoC platform

Change-Id: I96350fdf2cfbe65690572ac47165b013ca4b1ac8