Add support for Nios-II EPCS Controller core.

* Patch by Scott McNutt, 20 Oct 2004:
  Nios-II cleanups:
  - Add sysid command (Nios-II only).
  - Locate default exception trampoline at proper offset.
  - Implement I/O routines (readb, writeb, etc)
  - Implement do_bootm_linux