allow mkimage to build and run on Cygwin-hosted systems
* Patch by Frank Müller, 18 Sep 2003:
use bi_intfreq instead of bi_busfreq to compute fec_mii_speed in
cpu/mpc8xx/fec.c
* Patch by Pantelis Antoniou, 16 Sep 2003:
add tool to compute fileds in the PLPRCR register for MPC86x
