WD33C93 has only two registers, which often times aren't mapped to adjacent
bus space locations. Map them individually, instead.

The maximum FIFO depth on old WD33C93 parts is only 5, not 12 as on 93A and
93B. However, there appear to be issues using the maximum of 5 on old
parts, so 4 is it.

Enable Fast SCSI transfers for WD33C93B parts with appropriate input
clocks.

My Seagate ST32430N now sees about 50% greater throughput (about 97% as
fast as IRIX can push it). However, there appear

Enable Fast SCSI transfers for WD33C93B parts with appropriate input
clocks.

My Seagate ST32430N now sees about 50% greater throughput (about 97% as
fast as IRIX can push it). However, there appear to be other performance
issues with the driver as other disks perform significantly worse than they
should, with or without this change.

Reviewed by bjh21. Tested on my Indy and Challenge S.

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Move the sgimips "sbic" driver from arch/sgimips/hpc/sbic.c to
dev/ic/wd33c93.c. This may not be the best WD33C93 driver we've
got, but it's the most recently worked on and probably the most
portabl

Move the sgimips "sbic" driver from arch/sgimips/hpc/sbic.c to
dev/ic/wd33c93.c. This may not be the best WD33C93 driver we've
got, but it's the most recently worked on and probably the most
portable, so it seems like a good basis for further work (and in
particular an acorn26 driver for the Acorn SCSI card). There's
no functional change in this commit, and sgimips kernels still
compile.

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