registers are registers that overlap with others on many controllers, but
which may actually be distinct on some controllers. Right now, the two
shadows are:
- wd_status (usually overlaps wd_command)
- wd_features (usually overlaps wd_error)
Add a new helper function, wdc_init_shadow_regs(), used to initialize
the shadow register handles on controllers where they do actually overlap.
Partially from Jordan Rhody @ Wasabi Systems, Inc.
- wdc_xfer to ata_xfer
- channel_queue to ata_queue
and move them to <dev/ata/atavar.h> so they can be used by non-wdc ATA
controllers. Clean up the member names of these structures while at it.
wdc_drvprobe() function. wdc_drvprobe() is used if the controller
does not specify a custom one prior to calling wdcattach(). The
WDC_CAPABILITY_DRVPROBE bit is gone.
thorpej