Fix early board initialization for Cogent CSB272 board

* Patch by Ed Okerson, 3 Mar 2004:
  fix CFI flash writes for little endian systems

* Patch by Reinhard Meyer, 01 Mar 2004:
  generalize USB and IDE support for MPC5200 with according
  changes to IceCube.h and TOP5200.h
  add Am29LV256 256 MBit FLASH support for TOP5200 boards
  add info about USB and IDE to README