on the ALCOR2 and Pyxis. BWX is enabled iff:
- It hasn't been disabled by the user (patch `cia_use_bwx' or build cia.o
with the option "CIA_USE_BWX=0"),
- it's enabled in CIA_CSR_CNFG,
- we are running on an EV5-family processor,
- BWX is in the processor's capabilities mask.