registers. rationale:
- Netwave cards choke if we map i/o memory to >= 0x400
- even though, CIS tuple talks nothing about it
- it is not possible to specify range in pcmcia_io_map
- it would be very bad to do a try-and-error bus_space allocation for
i/o memory regions < 0x400
- we can have exactly the same functionality with memory mapped access
this should correct PR 10139.
the memory mapped access idea was from WIDE wildboar/bsdi cnw code.
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